Add a tip on code formatting in the "Contributing" docs

Also remove the warning on arm64 Docker building as it's now included in the Dockerfile

Signed-off-by: Thomas Druez <tdruez@nexb.com>

Author: tdruez

docs/contributing.rst

@@ -58,6 +58,10 @@ For more established contributors, you can contribute to the codebase in several
     and :ref:`faq` to confirm whether a given issue or a question has previously been
     discussed.
 
+.. tip::
+    Cleanup your code before submitting changes using the ``make valid``
+    command to ensure the proper code format and imports order.
+
 Documentation Improvements
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 

docs/installation.rst

@@ -42,12 +42,6 @@ create an **environment file**, and **build the Docker image**::
     make envfile
     docker-compose build
 
-.. warning::
-    If your host machine is based on Apple Silicon or another ARM64 architecture,
-    you need to force the platform to ``linux/amd64`` at build time using::
-
-        DOCKER_DEFAULT_PLATFORM=linux/amd64 docker-compose build
-
 .. note::
     You need to rebuild the image whenever ScanCode.io's source code has been
     modified or updated.