precise contribute

CONTRIBUTE.md

@@ -5,8 +5,11 @@
 * `2.x.x` main line for 2.x.x
 * `3.x.x` actual main line
     * documentation links refer to `3.x.x`
+    * 2.x.x can be merged to 3.x.x
 * `main`
     * documentation links refer to `latest`
+    * 3.x.x can be merged to main
+* `stable` main line for 2.x.x with release tags
 
 ## Testing
 
@@ -39,7 +42,19 @@ tox
 ### Release
 
 ```bash
-git pull
+# Update 3.x.x
+git checkout 3.x.x
+git pull origin 2.x.x
+git push origin 3.x.x
+
+# Update main
+git checkout main
+git pull origin 3.x.x
+git push origin main
+
+# Update release branch - currently 2.x.x
+git checkout stable
+git pull origin 2.x.x
 
 prev_version=$(poetry version -s)