Added copilot instructions for sdk release (Azure#51258)

Author: jeo02

.github/copilot-instructions.md

@@ -0,0 +1,19 @@
+## SDK release
+
+There are two tools to help with SDK releases:
+- Check SDK release readiness
+- Release SDK
+
+### Check SDK Release Readiness
+Run `CheckPackageReleaseReadiness` to verify if the package is ready for release. This tool checks:
+- API review status
+- Change log status
+- Package name approval(If package is new and releasing a preview version)
+- Release date is set in release tracker
+
+### Release SDK
+Run `ReleasePackage` to release the package. This tool requires package name and language as inputs. It will:
+- Check if the package is ready for release
+- Identify the release pipeline
+- Trigger the release pipeline.
+User needs to approve the release stage in the pipeline after it is triggered.