Add docstrings for array module

[sanketverma1704]

xref: #2215 and #2245

This PR adds docstrings for zarr.array module and builds on top of @e-marshall's #2276. I've added documentation for following functions:

• from_dict()
• getitem()
• setitem()
• resize()
• update_attributes()

I will start adding code examples soon. Feedback on the current draft would be greatly appreciated. Thanks!

[sanketverma1704]

pre-commit.ci autofix

[jhamman]

@MSanKeys963 - we just merged @e-marshall's PR so you can update this one and finish it off.

I think you can also skip docstrings for any method that start with _. So that should help limit the scope here.

[sanketverma1704]

Please review, @jhamman — my apologies for the delay.