Add .npmignore file to remove unneeded files from package

[ryan-roemer]

See https://github.com/FormidableLabs/urql/blob/master/.npmignore for a good whitelist-based approach.

For motivation, here's currently everything we'll bundle which is way more than we should:

$ npm install

$ npm build

$ npm pack
urql-devtools-0.0.1.tgz

$ tar -tvf urql-devtools-0.0.1.tgz 
-rw-r--r--  0 0      0        2550 Jul  4 13:01 package/package.json
-rw-r--r--  0 0      0         723 Jul  4 13:01 package/.eslintrc
-rw-r--r--  0 0      0          52 Jul  4 13:01 package/.huskyrc
-rw-r--r--  0 0      0          93 Jul  4 13:01 package/.lintstagedrc
-rw-r--r--  0 0      0         385 Jul  4 13:01 package/.sail.ci
-rw-r--r--  0 0      0         583 Jul  4 13:01 package/.sail.yml
-rw-r--r--  0 0      0        1089 Jul  4 13:01 package/README.md
-rw-r--r--  0 0      0          89 Jul  4 13:01 package/tsconfig.exchange.json
-rw-r--r--  0 0      0         241 Jul  4 13:01 package/tsconfig.json
-rw-r--r--  0 0      0        2801 Jul  4 13:01 package/webpack.config.js
-rw-r--r--  0 0      0        2127 Jul  4 13:01 package/.circleci/config.yml
-rw-r--r--  0 0      0        2123 Jul  4 13:04 package/dist/assets/icon-128.png
-rw-r--r--  0 0      0        3369 Jul  4 13:04 package/dist/assets/icon-192.png
-rw-r--r--  0 0      0        4147 Jul  4 13:04 package/dist/assets/icon-256.png
-rw-r--r--  0 0      0        9021 Jul  4 13:04 package/dist/assets/icon-512.png
-rw-r--r--  0 0      0        1001 Jul  4 13:04 package/dist/assets/icon.svg
-rw-r--r--  0 0      0        1902 Jul  4 13:04 package/dist/background.js
-rw-r--r--  0 0      0        7827 Jul  4 13:04 package/dist/background.js.map
-rw-r--r--  0 0      0        1383 Jul  4 13:04 package/dist/content_script.js
-rw-r--r--  0 0      0        5824 Jul  4 13:04 package/dist/content_script.js.map
-rw-r--r--  0 0      0          89 Jul  4 13:04 package/dist/devtools.html
-rw-r--r--  0 0      0        1123 Jul  4 13:04 package/dist/devtools.js
-rw-r--r--  0 0      0        4979 Jul  4 13:04 package/dist/devtools.js.map
-rw-r--r--  0 0      0        1912 Jul  4 13:03 package/dist/exchange.js
-rw-r--r--  0 0      0         898 Jul  4 13:04 package/dist/manifest.json
-rw-r--r--  0 0      0         115 Jul  4 13:04 package/dist/panel.html
-rw-r--r--  0 0      0      828923 Jul  4 13:04 package/dist/panel.js
-rw-r--r--  0 0      0     3201322 Jul  4 13:04 package/dist/panel.js.map
-rw-r--r--  0 0      0        1587 Jul  4 13:01 package/docs/Development.md
-rw-r--r--  0 0      0        2123 Jul  4 13:01 package/src/assets/icon-128.png
-rw-r--r--  0 0      0        3369 Jul  4 13:01 package/src/assets/icon-192.png
-rw-r--r--  0 0      0        4147 Jul  4 13:01 package/src/assets/icon-256.png
-rw-r--r--  0 0      0        9021 Jul  4 13:01 package/src/assets/icon-512.png
-rw-r--r--  0 0      0        1001 Jul  4 13:01 package/src/assets/icon.svg
-rw-r--r--  0 0      0        2064 Jul  4 13:01 package/src/background/background.ts
-rw-r--r--  0 0      0         238 Jul  4 13:01 package/src/codemirror.d.ts
-rw-r--r--  0 0      0         686 Jul  4 13:01 package/src/content_script.ts
-rw-r--r--  0 0      0          31 Jul  4 13:01 package/src/devtools/devtools.html
-rw-r--r--  0 0      0         245 Jul  4 13:01 package/src/devtools/devtools.ts
-rw-r--r--  0 0      0        2223 Jul  4 13:01 package/src/exchange.ts
-rw-r--r--  0 0      0         118 Jul  4 13:01 package/src/globals.d.ts
-rw-r--r--  0 0      0         817 Jul  4 13:01 package/src/manifest.json
-rw-r--r--  0 0      0         377 Jul  4 13:01 package/src/panel/App.css
-rw-r--r--  0 0      0        1277 Jul  4 13:01 package/src/panel/App.tsx
-rw-r--r--  0 0      0         311 Jul  4 13:01 package/src/panel/components/Background.tsx
-rw-r--r--  0 0      0          23 Jul  4 13:01 package/src/panel/components/index.ts
-rw-r--r--  0 0      0         807 Jul  4 13:01 package/src/panel/components/Tabs.tsx
-rw-r--r--  0 0      0         415 Jul  4 13:01 package/src/panel/components/Tag.tsx
-rw-r--r--  0 0      0        1549 Jul  4 13:01 package/src/panel/context/Devtools.tsx
-rw-r--r--  0 0      0        6413 Jul  4 13:01 package/src/panel/context/Events.tsx
-rw-r--r--  0 0      0          81 Jul  4 13:01 package/src/panel/context/index.ts
-rw-r--r--  0 0      0        2305 Jul  4 13:01 package/src/panel/context/Request.tsx
-rw-r--r--  0 0      0        4485 Jul  4 13:01 package/src/panel/events/EventCard.tsx
-rw-r--r--  0 0      0        1712 Jul  4 13:01 package/src/panel/events/Events.tsx
-rw-r--r--  0 0      0        3009 Jul  4 13:01 package/src/panel/events/Filters.tsx
-rw-r--r--  0 0      0          26 Jul  4 13:01 package/src/panel/events/index.ts
-rw-r--r--  0 0      0          25 Jul  4 13:01 package/src/panel/events/panels/index.ts
-rw-r--r--  0 0      0         911 Jul  4 13:01 package/src/panel/events/panels/JsonCode.tsx
-rw-r--r--  0 0      0        1711 Jul  4 13:01 package/src/panel/events/panels/Panel.tsx
-rw-r--r--  0 0      0         703 Jul  4 13:01 package/src/panel/events/panels/QueryPanel.tsx
-rw-r--r--  0 0      0         981 Jul  4 13:01 package/src/panel/Navigation.tsx
-rw-r--r--  0 0      0          60 Jul  4 13:01 package/src/panel/panel.html
-rw-r--r--  0 0      0         143 Jul  4 13:01 package/src/panel/panel.tsx
-rw-r--r--  0 0      0        2724 Jul  4 13:01 package/src/panel/request/Query.tsx
-rw-r--r--  0 0      0         693 Jul  4 13:01 package/src/panel/request/Request.tsx
-rw-r--r--  0 0      0        1567 Jul  4 13:01 package/src/panel/request/Response.tsx
-rw-r--r--  0 0      0        1565 Jul  4 13:01 package/src/panel/types.ts
-rw-r--r--  0 0      0           0 Jul  4 13:01 package/src/panel/utils.ts
-rw-r--r--  0 0      0         768 Jul  4 13:01 package/src/styled-components.d.ts
-rw-r--r--  0 0      0         697 Jul  4 13:01 package/src/types.ts