Update dockerignore to include dev dir

This is so that CI can build an image that includes the dev folder, which has the exmaple bot.

This also removes the test and docs folders, as they od not need to be in a built image.

Author: ChrisLovering

.dockerignore

@@ -1,9 +1,7 @@
 *
 
 !pydis_core/
-!docs/
-!tests/
-
+!dev/
 !pyproject.toml
 !poetry.lock
-!tox.ini
+!README.md