chore: add README

README.md

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+# Actism
+
+Run Extism plug-ins as a pipeline on GitHub Actions. 
+
+### Example
+
+
+```yaml
+name: test action
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  ci_example_pipelines:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dylibso/actism@main
+        id: actism-image
+        with:
+          wasi: true
+          input: "this is a test"
+          output_type: text
+          steps: |- # line-delimited set of named plugin calls, where "step()" export is ran
+            count vowels | https://github.com/extism/plugins/releases/latest/download/count_vowels.wasm | count_vowels
+            convert output to image data | https://cdn.modsurfer.dylibso.com/api/v1/module/271d6599df5fc1c54ddc33c266840123636d2c886e5064a739324f92ae8fc5ac.wasm
+            generate png | https://cdn.modsurfer.dylibso.com/api/v1/module/2c9eb901052b1e6397d2414bdb796975407cc87085e6b5fe9564932538d8af51.wasm | handle
+      - name: check output
+        run: |
+          echo '${{steps.actism-image.outputs.output}}' | jq '.value' | base64 -d -i > out.png
+      - uses: actions/upload-artifact@v4
+        with:
+          name: out.png
+          path: ./out.png
+
+      - uses: ./
+        id: actism-text
+        with:
+          wasi: true
+          input: "this is a test"
+          output_type: text
+          steps: |- # line-delimited set of named plugin calls, where "step()" export is ran
+            count vowels | https://github.com/extism/plugins/releases/latest/download/count_vowels.wasm | count_vowels
+      - name: check output
+        run: |
+          echo '${{steps.actism-text.outputs.output}}' | grep '"count":4'
+```
+
+The above step with `id` "actism-image" will count the vowels in the input, convert that to a known format for the image generator, and then use the total count from the first plugin to generate an image with the value encoded. Then the output (out.png) will be uploaded to the summary artifacts on the Action run. 
+
+You can combine Extism plug-ins and arbitrary GitHub Action steps to execute pipelines to do anything.
+
+## Next Steps
+
+The Extism plug-ins should get host functions that wrap the convenient `@actions/core` and `@actions/github` JavaScript package functions, so a plug-in could interact with GitHub Actions more directly.