docs: add development guide including one first guideline wrt lua vs. sh usage (#951)

docs/dev/basics.rst

@@ -47,3 +47,12 @@ and you can try rebasing it onto the new `base` branch yourself and after that c
 
 Always call `make update-patches` after making changes to a module repository as `make update` will overwrite your
 commits, making `git reflog` the only way to recover them!
+
+Development Guidelines
+----------------------
+lua should be used instead of sh whenever sensible. The following criteria
+should be considered:
+
+- Is the script doing more than just executing external commands? if so, use lua
+- Is the script parsing/editing json-data? If so, use lua for speed
+