chore: add instruction of generating changelog from last release (#1405)

**Motivation:**

add instruction of how to generate changelog from last release

**Modifications:**

add instruction of how to generate changelog from last release

**Result:**

add instruction of how to generate changelog from last release

Author: bowenli86

CHANGELOG/CHANGELOG-template.md

@@ -35,9 +35,50 @@ github handle of release manager
 
 ## Changelog
 
-Copy the one that's auto generated from github by default to here, and submit PR for review
+To generate a changelog of commits added since the last release using Git on 
+the command line, follow these steps:
 
+1. Identify the last release tag
 
-- merged PRs in diff from last release
-- contributors
-- etc
+First, list your tags (assuming you use Git tags for releases):
+
+```
+git tag --sort=-creatordate
+```
+
+This shows your most recent tags at the top. Let's say the last release tag is `v1.4.2`
+
+
+2. Generate the changelog
+
+Now, use the following command to list the commits since that tag, and auto generate github PR link if there's any
+
+```
+git log v1.4.2..HEAD --pretty=format:"%s" --no-merges | \
+sed -E 's/^(.*)\(#([0-9]+)\)$/- \1[PR #\2](https:\/\/github.com\/layr-labs\/eigenlayer-contracts\/pull\/\2)/' | \
+sed -E '/\[PR #[0-9]+\]/! s/^(.*)$/- \1/'
+```
+
+This will show:
+
+- Only commits since v1.4.2 up to the current HEAD
+- One-line commit messages (%s) with the author name (%an)
+
+
+An example output is:
+
+```
+- ci: add explicit permissions to workflows to  mitigate security concerns [PR #1392](https://github.com/layr-labs/eigenlayer-contracts/pull/1392)
+- ci: remove branch constraint for foundry coverage job
+- docs: add release managers to changelogs
+- docs: add templates for changelog and release notes [PR #1382](https://github.com/layr-labs/eigenlayer-contracts/pull/1382)
+- docs: add doc for steps to write deploy scripts [PR #1380](https://github.com/layr-labs/eigenlayer-contracts/pull/1380)
+- ci: add testnet envs sepolia and hoodi to validate-deployment-scripts [PR #1378](https://github.com/layr-labs/eigenlayer-contracts/pull/1378)
+- docs: update MAINTENANCE to include practices of merging multiple release-dev branches
+- docs: updating readme for dead links, readability, new language, and more [PR #1377](https://github.com/layr-labs/eigenlayer-contracts/pull/1377)
+...
+```
+
+3. Commit the Changelog
+
+Copy the output and add here with a commit, then proceed to cut the release from the commit.