Have some release guideline (#694)

* release guideline

* better in another file

Author: gui1117

RELEASE.md

@@ -0,0 +1,10 @@
+## Release process
+
+1. Update the version `[workspace.package]` in `Cargo.toml`.
+2. Update the version of `parity-scale-codec-derive` dependency for `parity-scale-codec` in `Cargo.toml`
+   (`parity-scale-codec-derive = { .., version = "=x.y.z", ...}`).
+3. Test the new release on `polkadot-sdk`, ensure `parity-scale-codec-derive` is also updated when testing.
+4. Update the `CHANGELOG.md`.
+5. Merge all these changes to master.
+6. Add and push a git tag with the version number: `git tag "vX.Y.Z"; git push --tags`.
+7. Publish on `crates.io` the package `parity-scale-codec-derive` and then `parity-scale-codec`.