Standardize "Bevy" capitalization

[BD103]

I've been noticing a lot of inconsistency between capitalized "Bevy" and lowercase "bevy". We should decide on one and standardize it throughout our documentation (in a follow-up, ofc!).

Originally posted by @BD103 in #1605 (comment)

[BD103]

Pasting @TrialDragon's comments in here:

The difference is when we're referring to Bevy, the proper noun, and bevy, the name of the specific GitHub repository in which the engine lives. At least in this case.

Probable best way to deal with this is encapsulating all the repository references (e.g., bevy, bevy-website, etc.) in backticks ``, AKA single-line code blocks.

EDIT: This has, at least initially, been done in this PR. I may have missed stuff. Still a good idea to keep the follow-up issues open for standardizing the rest of the site if need be.

[alice-i-cecile]

I agree with the style chosen by @TrialDragon there.