doc: more "s" to "S" in visual mode, and fix a typo

[ChrisJohnsen]

I found a few more mentions of using s while in visual mode. The first commit changes them to the supported S mapping.

The second commit fixes a stray typo I found: “like” for “line”.

I used two commits since the changes are logically separate, but I can squash them if you would like that better.

[tpope]

Thanks!

[Huxpro]

May I remap back to use s in visual mode rather than S? I found spacemacs also use that convention. Out of curiosity, what're the problems ppl mentioned about using s in visual mode? I found I seldom used s and dominantly uses c.