Documentation Updates as per #697

[MTwem]

This update addresses issues raised in #697 :

"https://rubicon-objc.beeware.org/en/latest/reference/rubicon-objc-types/#rubicon.objc.types.register_preferred_encoding there's ":func:register_encoding" reference instead of linked correctly.

Also NSEdgeInsetsMake at https://rubicon-objc.beeware.org/en/latest/reference/rubicon-objc-types/#rubicon.objc.types.NSEdgeInsetsMake is missing a docstring.

[freakboy3742]

Thanks for this update; a couple of notes inline, in addition to the pre-commit issue that CI has flagged.

[freakboy3742]

The change note isn't the same thing as a commit message - it's the content that will be put into the final release notes. That means it needs to be in a voice of "Rubicon now has long awaited shiny new feature!" or "Rubicon no longer breaks on Tuesday afternoons".

In this case, it probably doesn't even rate a release note - although this is a change to documentation, it's a relative minor bugfix/tweak, not something is an important update that someone upgrading should know about.

To that end - this file should:

1. Be named 697.misc.md
2. Only include the text "Some minor errors in ObjC type documentation were resolved.".

[freakboy3742]

The docstring for other ...Make() methods is indicative here. We don't need to declare parameters (and if we did, we would use Sphinx notation); and the reference to NSEdgeInserts should be a cross-reference, not a RST literal.

[MTwem]

Comments actioned. Ready for review

[freakboy3742]

Tere was one last pre-commit issue caused by a trailing space on a line; I've corrected that, and tests have now passed. Thanks for the PR!

[MTwem]

Hooray! My first issue