merge: split our contribution guidelines in their own file (!1147)

View MR for information: https://activitypub.software/TransFem-org/Sharkey/-/merge_requests/1147

Approved-by: Hazelnoot <acomputerdog@gmail.com>
Approved-by: Luna <her@mint.lgbt>

packages/backend/test/compose.yml

@@ -2,12 +2,12 @@ services:
   redistest:
     image: redis:7
     ports:
-      - "127.0.0.1:56312:6379"
+      - "127.0.0.1:6379:6379"
 
   dbtest:
-    image: postgres:15
+    image: postgres:17
     ports:
-      - "127.0.0.1:54312:5432"
+      - "127.0.0.1:5432:5432"
     environment:
       POSTGRES_DB: "test-misskey"
       POSTGRES_HOST_AUTH_METHOD: trust