docs: add note on how to release

Author: MultisampledNight

MAINTAIN.md

@@ -0,0 +1,12 @@
+# Maintenance
+
+## How to release
+
+1. Commit everything and push everything you want in the release
+2. Run `util/release.sh`
+3. Bump the version number in
+  - `typst.toml`
+  - `template/main.typ`
+  - `README.md`
+
+That's it!