Add a link the different possible Android virtual device configs (flu…

…tter#142765)

*Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.*

*List which issues are fixed by this PR. You must list at least one issue. An issue is not required if the PR fixes something trivial like a typo.*

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*

.ci.yaml

@@ -35,6 +35,9 @@ platform_properties:
       os: Ubuntu
       cores: "8"
       device_type: none
+  # The current android emulator config names can be found here:
+  # https://chromium.googlesource.com/chromium/src.git/+/HEAD/tools/android/avd/proto
+  # You may use those names for the android_virtual_device version.
   linux_android_emu:
     properties:
       contexts: >-