Add branch instructions in CONTRIBUTING.md and Update ADO pipeline triggers (#78)

* dev branch

* update ado trigger

Author: doctorlai-msrc

CONTRIBUTING.md

@@ -17,6 +17,9 @@ or contact [[email protected]](mailto:[email protected]) with any addi
 
 We welcome contributions from everyone. The following guidelines will help you understand our expectations and streamline the review process.
 
+## Branch
+All PRs should be made against the `dev` branch. Please ensure your branch is up to date with the latest changes before submitting a pull request. And the `main` branch is used for release. Consider `main` as the stable branch and `dev` as the development branch.
+
 ## Code Style
 
 We follow the LLVM coding style for all C/C++ code. Please ensure your code conforms to this style. To automate this process, we use `clang-format`:

azure-pipelines.yml

@@ -2,13 +2,13 @@ trigger:
   branches:
     include:
       - main
-      - stable
       - gh-readonly-queue/main/*
+      - dev
 
 pr:
   branches:
     include:
-      - '*'
+      - main
 
 pool:
   name: agent-pool-onprem-ubuntu