Bug(docs): we're missing netlify logout command from the docs and help

[erezrokah]

1. Goto https://cli.netlify.com/, see that the logout command is missing
2. Run netlify help - see that it doesn't print the logout command in the console.

Related to #660 (comment).

Not sure why, but hiding the command seems intentional:

cli/src/commands/logout.js

Line 34 in 01b3419

LogoutCommand.hidden = true

[Xenonym]

According to #141, the logout command was hidden two years ago (emphasis mine):

Hide logout command

Since we started going down the multi-user path, logout doesn’t actually log you out. We should prioritize getting user switching in soon after the launch.

[erezrokah]

Since a user can revoke the CLI access token in the UI, we should look into doing the same thing when a user logs out: