Changelog check (#1047)

* Add changelog check

Author: 3Rafal

.github/workflows/changelog.yml

@@ -0,0 +1,13 @@
+name: Changelog check
+
+on:
+  pull_request:
+    branches: [ main ]
+    types: [ opened, synchronize, reopened, labeled, unlabeled ]
+
+jobs:
+  Changelog-Entry-Check:
+    name: Check Changelog Action
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: tarides/changelog-check-action@v1

README.md

@@ -327,6 +327,12 @@ make all
 # the ocamllsp executable can be found at _build/default/ocaml-lsp-server/bin/main.exe
 ```
 
+### Changelog
+
+User-visible changes should come with an entry in the changelog under the appropriate part of 
+the **unreleased** section. PR that doesn't provide an entry will fail CI check. This behavior 
+can be overridden by using the "no changelog" label, which is used for changes that are not user-visible.
+
 ## Tests
 
 To run tests execute: