Docs: add a living faq document for sharing dev solutions (#3156)

* adding one faq :)

* adding another faq that links to the relevant file

* add lined line breaks between questions and lower the heading size of the question so sub-divisions can be added later

* missed some newlines

* updating best practice filler method

* add note about get_filler_item_name()

* updates to wording from review

* add section to CODEOWNERS for maintainers of this doc

* use underscores to reference the file easier in CODEOWNERS

* update link to be direct and filter to function name

docs/apworld_dev_faq.md

@@ -0,0 +1,32 @@
+# APWorld Dev FAQ
+
+This document is meant as a reference tool to show solutions to common problems when developing an apworld.
+
+---
+
+### My game has a restrictive start that leads to fill errors
+
+Hint to the Generator that an item needs to be in sphere one with local_early_items
+```py
+early_item_name = "Sword"
+self.multiworld.local_early_items[self.player][early_item_name] = 1
+```
+
+---
+
+### I have multiple settings that change the item/location pool counts and need to balance them out
+
+In an ideal situation your system for producing locations and items wouldn't leave any opportunity for them to be unbalanced. But in real, complex situations, that might be unfeasible.
+
+If that's the case, you can create extra filler based on the difference between your unfilled locations and your itempool by comparing [get_unfilled_locations](https://github.com/ArchipelagoMW/Archipelago/blob/main/BaseClasses.py#:~:text=get_unfilled_locations) to your list of items to submit
+
+Note: to use self.create_filler(), self.get_filler_item_name() should be defined to only return valid filler item names
+```py
+total_locations = len(self.multiworld.get_unfilled_locations(self.player))
+item_pool = self.create_non_filler_items()
+
+while len(item_pool) < total_locations:
+    item_pool.append(self.create_filler())
+
+self.multiworld.itempool += item_pool
+```