Applying prettier in CI for pusher and back containers

.github/workflows/continuous_integration.yml

@@ -64,6 +64,11 @@ jobs:
         run: yarn test
         working-directory: "front"
 
+ # We will enable prettier checks on front in a few month, when most PRs without prettier have been merged
+ #     - name: "Prettier"
+ #       run: yarn run pretty-check
+ #       working-directory: "front"
+
   continuous-integration-pusher:
     name: "Continuous Integration Pusher"
 
@@ -107,6 +112,10 @@ jobs:
         run: yarn test
         working-directory: "pusher"
 
+      - name: "Prettier"
+        run: yarn run pretty-check
+        working-directory: "pusher"
+
   continuous-integration-back:
     name: "Continuous Integration Back"
 
@@ -150,3 +159,7 @@ jobs:
         run: yarn test
         working-directory: "back"
 
+      - name: "Prettier"
+        run: yarn run pretty-check
+        working-directory: "back"
+

CONTRIBUTING.md

@@ -46,6 +46,15 @@ $ yarn run install
 $ yarn run prepare
 ```
 
+If you don't have the precommit hook installed (or if you committed code before installing the precommit hook), you will need 
+to run code linting manually:
+
+```console
+$ docker-compose exec front yarn run pretty
+$ docker-compose exec pusher yarn run pretty
+$ docker-compose exec back yarn run pretty
+```
+
 ### Providing tests
 
 WorkAdventure is based on a video game engine (Phaser), and video games are not the easiest programs to unit test.