Document vendordep gradle task

[Starlight220]

Accompanies wpilibsuite/GradleRIO#418.
Draft until the above commit is merged.

[Starlight220]

@Daltz333 , can you mark this as ready for review and Waiting on dependency?

[Daltz333]

Can you merge master?

[Starlight220]

Won't merge add the 40 commits to this PR? If so, was there a problem with the rebase?

[Starlight220]

Anyway, this is waiting on wpilibsuite/GradleRIO#418 so it isn't going anywhere and will probably need to be updated then. Can you mark this as Waiting on: Dependency/WPILib?

[Daltz333]

Could you merge or rebase onto master?

[Starlight220]

@ThadHouse can you make sure I haven't made any technical mistakes in the docs?

[Starlight220]

I haven't noticed that the whole article had been reworked. Maybe the section I'm adding should be added somewhere/somehow else in the article?

[Daltz333]

The article hasn't been reworked, just moved around. I'm fine with merging this mostly as is (see my comment), as I can just incorporate the information into a revision later. My goal is to better integrate using CAN devices into the zero-to-robot as that's what the overwhelming majority of teams use as their main motor controllers.