Update branch details in CONTRIBUTING.md

CONTRIBUTING.md

@@ -23,9 +23,17 @@ reported the issue. Please try to include as much information as you can. Detail
 ## Contributing via Pull Requests
 Contributions via pull requests are much appreciated. Before sending us a pull request, please ensure that:
 
-1. You are working against the latest source on the *master* branch.
-2. You check existing open, and recently merged, pull requests to make sure someone else hasn't addressed the problem already.
-3. You open an issue to discuss any significant work - we would hate for your time to be wasted.
+1. You are working against the latest source on the correct branch.
+ Amazon Linux 2022 releases are made from the *main* branch, while
+ Amazon Linux 2 releases are made from the *1.x* branch. Your pull
+ requests should target the branch appropriate to the distribution
+ you're targeting with your improvement. If you are targeting a
+ distribution other than Amazon Linux, you should most likely be
+ working on the *main* branch.
+2. You check existing open, and recently merged, pull requests to make
+ sure someone else hasn't addressed the problem already.
+3. You open an issue to discuss any significant work - we would hate
+ for your time to be wasted.
 
 To send us a pull request, please: