docs: replace stage file example in /install/completion, fix typos found in review

[jeremydesroches]

Found in review for #1743. Replaced out-of-date dvc repro stage file example with dvc plots completion example.

[jeremydesroches]

@jorgeorpinel for the other docs listed in #1743, do you prefer that I compile all updates in this PR or separately?

[jorgeorpinel]

Small PRs are preferred @jeremydesroches thanks. BTW you don't need to address everything in #1743. It's good practice so it would be good for you to get a few in each category, but it doesn't seem that related to your GSoD project [SEO, keywords, etc]. Thanks!

[jeremydesroches]

I understand. I'll do a few this week and then move on to SEO-focussed items only.

[jeremydesroches]

Hey @jorgeorpinel, I added a few fixes for simple typos found along the way in completing the review for #1743. Will leave the other open items in #1743 for other PRs.

[jorgeorpinel]

I highly doubt the autocompletion tool reads stages from dvc.yaml files. It probably only works with .dvc files. In fact it probably completes any file path. Please try it. Editing most of these docs usually involves actually trying the tool in question. Thanks

[jeremydesroches]

OK. I see you mentioned trying the tool here. Yeah it's not that smart probably. You can just say something like "existing files" here.

Yes, this was the motivation for replacing the dvc repro example in the first place. It didn't complete with stages from dvc.yaml. It does complete with .dvc files so "existing files" makes sense.

[jorgeorpinel]

2 small things pending above but this is good overall. Thanks

p.s. Let's avoid adding more unrelated changes here but feel free to open other PRs as needed.

[jorgeorpinel]

Thanks @jeremydesroches