Sync CONTRIBUTING.md with .github copy (#106677)

Author: Hixie

CONTRIBUTING.md

@@ -8,11 +8,11 @@ _tl;dr: join [Discord](https://github.com/flutter/flutter/wiki/Chat), be [courte
 Welcome
 -------
 
-We invite you to join our team! Everyone is welcome to contribute code
-via pull requests, to file issues on GitHub, to help people asking for
-help on our mailing lists, our chat channels, or on Stack Overflow, to
-help triage, reproduce, or fix bugs that people have filed, to add to our
-documentation, or to help out in any other way.
+We invite you to join the Flutter team, which is made up of volunteers and sponsored folk alike!
+There are many ways to contribute, including writing code, filing issues on GitHub, helping people
+on our mailing lists, our chat channels, or on Stack Overflow, helping to triage, reproduce, or
+fix bugs that people have filed, adding to our documentation,
+doing outreach about Flutter, or helping out in any other way.
 
 We grant commit access (which includes full rights to the issue
 database, such as being able to edit labels) to people who have gained
@@ -35,7 +35,7 @@ Before you get started, we encourage you to read these documents which describe
 Helping out in the issue database
 ---------------------------------
 
-Triage is the process of going through bugs and determining if they are valid, finding out
+Triage is the process of going through bug reports and determining if they are valid, finding out
 how to reproduce them, catching duplicate reports, and generally making our issues list
 useful for our engineers.
 
@@ -68,16 +68,20 @@ If you want to help us triage, you are very welcome to do so!
 Quality Assurance
 -----------------
 
-One of the most useful tasks, closely related to triage, is finding and filing bugs. Testing
+One of the most useful tasks, closely related to triage, is finding and filing bug reports. Testing
 beta releases, looking for regressions, creating test cases, adding to our test suites, and
 other work along these lines can really drive the quality of the product up. Creating tests
 that increase our test coverage, writing tests for issues others have filed, all these tasks
 are really valuable contributions to open source projects.
 
-If this interests you, you can jump in and submit bugs without needing anyone's permission!
-The #hackers-tests channel on our [Discord server](https://github.com/flutter/flutter/wiki/Chat)
-is a good place to talk about what you're doing. If you want to contribute test cases, you
-can also submit PRs, see the next section for how to set up your development environment.
+If this interests you, you can jump in and submit bug reports without needing anyone's permission!
+The #qa channel on our [Discord server](https://github.com/flutter/flutter/wiki/Chat)
+is a good place to talk about what you're doing. We're especially eager for QA testing when
+we announce a beta release. See https://github.com/flutter/flutter/wiki/Quality-Assurance for
+more details.
+
+If you want to contribute test cases, you can also submit PRs. See the next section
+for how to set up your development environment, or ask in #hackers-test on Discord.
 
 > As a personal side note, this is exactly the kind of work that first got me into open
 > source. I was a Quality Assurance volunteer on the Mozilla project, writing test cases for