document release steps (#75)

RELEASE.md

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+## How to make a new release
+
+
+1. `git pull` - make sure your local checkout is up to date
+2. Ensure changelog entries exist for all relevant changes.
+3. Make a new version in the changelog -> semver + some title that roughly describes the changes
+4. update version in `Cargo.toml` and in `message_parser_wasm/Cargo.toml`. (if you run rust-analyzer then `Cargo.lock` is updated automatically)
+5. make a commit with the changes "prepare <version>"
+6. make a tag for the version
+7. push both commit and tag
+8. run `cargo publish`
+9. run `cd message_parser_wasm && wasm-pack build --scope deltachat --target web && wasm-pack publish --target web`
+10. make a release on github, copy the changelog for that version over to there