Move doc to RELEASE.md

Author: kimwalisch

doc/Development_Guide.md

@@ -0,0 +1,12 @@
+## How to do a new libdivide release
+
+Releases are semi-automated using GitHub actions:
+
+1. Manually run the [Create draft release](https://github.com/ridiculousfish/libdivide/actions/workflows/prepare_release.yml) workflow/action.
+    * This does some codebase housekeeping and creates a draft release.
+    * This updates the version numbers in ```libdivide.h```, ```CMakeLists.txt```, ... and creates a new commit.
+    * This creates a new git tag of format vX.Y.Z. 
+2. Follow the output link in the action summary to the generated draft release. E.g. ![image](https://github.com/user-attachments/assets/7e8393f7-f204-4b3a-af37-de5e187479dc)
+3. Edit the generated release notes as needed & publish
+
+Note that PRs with the ```ignore-for-release``` label are excluded from the generated release notes.