Update TRIAGE and CONTRIBUTING docs

Author: elliette

CONTRIBUTING.md

@@ -154,6 +154,12 @@ not want to merge `upstream/master` or update your Flutter SDK version, instead
     If the version of DCM used on the bots is outdated, consider contributing a
 	PR to update the version on the bots to the latest.
 
+## Companion app
+
+For most DevTools features, we recommend using the [DevTools companion
+app](https://github.com/flutter/demos/tree/main/devexp_demos/devtools_companion)
+as the example Flutter app to connect to when working on DevTools.
+
 ## Running and debugging DevTools
 
 Please see [DEBUGGING.md]() for guidance on running and debugging DevTools.

TRIAGE.md

@@ -27,7 +27,7 @@ by applying [proper labels](#label-the-issue) and [assigning priority](#prioriti
 Transfer any issues to the `flutter/devtools` repo that should be tracked on our own issue tracker, and close issues you
 find that are obsolete.
 4. Try to reproduce any issues with the [reproduce to verify](https://github.com/flutter/devtools/labels/reproduce%20to%20verify) label.
-5. Spend at least 20 minutes [cleaning up the issue backlog](#clean-up-the-issue-backlog).
+5. Spend at least 20 minutes [cleaning up the issue backlog](#clean-up-the-issue-backlog) and/or labeling backlog issues with "contributions welcome" or "good first issue".
 6. Look through the DevTools discord [channel](https://discord.com/channels/608014603317936148/958862085297672282) for any recent user
 questions or concerns that require a response.
 
@@ -36,9 +36,11 @@ questions or concerns that require a response.
 * Add labels for its proper category or categories ( “screen: inspector", “screen: network", “bug”, etc.)
 * Add cost labels ("cost: low", "cost: medium", etc.) if you have a good idea of how much work it will
 take to resolve this issue. Leave the cost label off if you do not know.
-* Add label “waiting for customer response” if you requested more details from reporter
-* Add label “fix it friday” if the issue should be fixed and looks easy to fix
-* Add label "good first issue" if the issue looks like an easy starter bug for a new contributor
+* Add label "waiting for customer response" if you requested more details from reporter.
+* Add label "contributions welcome" for issues that can be tackled by the community.*
+* Add label "good first issue" if the issue looks like an easy starter bug for a new contributor.*
+
+> [*] In our contribution guidelines we suggest that contributors use the "contributions welcome" and "good first issue" labels to find issues to work on. Therefore, it is important to keep these lists well-populated.
 
 ### Prioritize the issue