docs: add detailed git steps for submitting PR and syncing branches in CONTRIBUTING (#1330)

**Motivation:**

add detailed git steps for submitting PR and syncing branches in
CONTRIBUTING

**Modifications:**

include detailed git steps for submitting PR and syncing branches in
CONTRIBUTING

**Result:**

include detailed git steps for submitting PR and syncing branches in
CONTRIBUTING

Author: bowenli86

CONTRIBUTING.md

@@ -136,41 +136,60 @@ upstream  https://github.com/Layr-Labs/eigenlayer-contracts.git (fetch)
 upstream  https://github.com/Layr-Labs/eigenlayer-contracts.git (push)
 ```
 
-### Make Sure Your Fork Is In Sync With Upstream
 
-Go to `main` branch in your fork repository
+### Create Your PR to Upstream Branches
+
+The following applies if you submit a PR to upstream branch of either `main` or `release-dev/*`, which will refer to as `<upstream-target-branch>`
+
+Create a local branch from the upstream branch:
 
 ```
-git checkout main
+git checkout -B <my-local-feature-branch> upstream/<upstream-target-branch>
 ```
 
-Fetch latest update from upstream
+Make your changes, then commit:
 
 ```
-git fetch upstream
+git add .
+git commit -m "your message"
 ```
 
-Rebase your `main` to the upstream `main`
+Push to your fork:
 
 ```
-git rebase upstream/main
+git push -u origin <my-local-feature-branch>
 ```
 
-Push to your fork repository
+Go to GitHub, and open a PR from:
 
 ```
-git push
+your-fork:<my-local-feature-branch>
+**to**
+Layr-Labs/eigenlayer-contracts:<upstream-target-branch>
 ```
 
-Now `main` in your fork repository should match the `main` in EigenLayer repository.
+GitHub should auto-detect this if branches match.
+
+If you already have an open PR for this branch, just push more commits to `<my-local-feature-branch>`, and the PR will update.
+
+
+### Keeping Your Branch Updated With Upstream
+
+To stay in sync with upstream's `<upstream-target-branch>`, whether it's `main` or `release-dev/*`:
+
+```
+git fetch upstream
+git checkout <my-local-feature-branch>
+git rebase upstream/<upstream-target-branch>
+
+# or use merge if you prefer
+# git merge upstream/<upstream-target-branch>
+
+git push -f origin <my-local-feature-branch>
+```
 
-### Create Your PR
+Use --force only if you're rebasing (not with merges).
 
-1. Create a new branch from your target upstream branch in your fork repository
-2. Make your code changes
-3. Commit your changes
-4. Push to your forked repository
-5. Create a PR from your branch to the appropriate branch in the upstream repository
 
 ### PR Title Format