Remove instances of $ from commands that don't include output

[alexakreizinger]

standard docs practices recommend not including $ in command snippets unless that snippet includes both input and output, in which case $ helps differentiate the two. (common linting tools like markdownlint include rules designed to find and fix this.)

this PR removes instances of $ from snippets that don't include output. in other words:

---

$ command

becomes

command

---

and

$ command1
$ command2

becomes

command1
command2

---

but

$ command
output
more output

remains the same.

[cnorris-cs]

I left suggestions, but I've added my approval based on that to keep this moving.