docs: mention conventional commits (#1490)

Also add build type to the allowed types.

.github/workflows/check_pr_title.yml

@@ -7,11 +7,9 @@ on:
 jobs:
   check_title:
     runs-on: ubuntu-20.04
-    permissions:
-      pull-requests: write
     steps:
       - uses: ytanikin/PRConventionalCommits@1.2.0
         with:
-          task_types: '["feat","fix","docs","test","ci","style","refactor","perf","chore","revert"]'
+          task_types: '["build","feat","fix","docs","test","ci","style","refactor","perf","chore"]'
           add_label: true
-          custom_labels: '{"feat":"enhancement", "fix":"bug", "docs":"documentation", "test":"testability", "ci":"ci", "style":"refactoring", "perf":"performance", "chore":"tooling"}'
+          custom_labels: '{"build":"build", "feat":"enhancement", "fix":"bug", "docs":"documentation", "test":"testability", "ci":"ci", "style":"refactoring", "refactor":"refactoring", "perf":"performance", "chore":"tooling"}'

CONTRIBUTING.md

@@ -72,6 +72,9 @@ git push --force
 Clio uses `ccache` to speed up compilation. If you want to use it, please make sure it is installed on your machine.
 CMake will automatically detect it and use it if it is available.
 
+## Opening a pull request
+When a pull request is open CI will perform checks on the new code.
+Title of the pull request and squashed commit should follow [conventional commits specification](https://www.conventionalcommits.org/en/v1.0.0/).
 
 ## Fixing issues found during code review
 While your code is in review, it's possible that some changes will be requested by reviewer(s).