Fix #8 Immutable Releases upd readme, add contributing

Author: boly38

.github/CONTRIBUTING.md

@@ -0,0 +1,33 @@
+[ < Back](../README.md)
+
+# HowTo Contribute
+
+Please create an [issue](https://github.com/boly38/action-mongo-tools/issues) describing your goal / question / bug description...
+
+If you're interested in an existing issue, please contribute by up-voting for it by adding a :+1:.
+
+If you want to push some code :
+- fork and prepare a feature-git-branch, then create a [pull request](https://github.com/boly38/action-mongo-tools/pulls) that link your issue.
+- execute test
+
+You could also be critic with existing ticket/PR : all constructive feedbacks are welcome.
+
+## test
+* cf. [TESTING.md](../TESTING.md)
+
+
+# Maintainer HowTos
+
+## HowTo create a fresh version
+- install github client
+- create automatically a draft release version using [gh client](https://cli.github.com/) 
+
+Example to create v1.0.3
+```bash
+gh release create v1.0.3 --draft --generate-notes
+```
+
+this will make a new draft release. Verify it in [releases list](https://github.com/boly38/action-mongo-tools/releases)
+
+- ⚠️ the repository apply immutable releases since #8, so you can't modify a release once published
+- publish the release when ready

README.md

@@ -31,5 +31,11 @@ env:
   MONGOTOOLS_KEEP_MAN: true
 ```
 
+# Immutable releases 
+
+For security reason, since #8, this repository rely on [immutable releases](https://docs.github.com/en/code-security/supply-chain-security/understanding-your-software-supply-chain/immutable-releases). 
+Instead of using `@stable` as tag, you could rely on fixed immutable release (ex. `@v1.0.4`). 
+
 # contributing
-PRs extending the functionality are welcome and will be reviewed.
+- PRs extending the functionality are welcome and will be reviewed.
+- more details on [CONTRIBUTING](./.github/CONTRIBUTING.md) and [TESTING](./TESTING.md)