Small content tweaks and additions to documentation

[hiAndrewQuinn]

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Hey, the link above https://bit.ly/atom-docs is 404'ing on me.

This is an extremely small content change to update the documentation. In Tree View, Shift+A adds folders specifically, and A adds files specifically. As someone who likes to read through documentation and memorize his keyboard shortcuts, I thought this would be a good, tiny thing to note in Atom Basics.

[hiAndrewQuinn]

I have just checked by rebuilding the Flight Manual locally, and the change I made appears correctly.

[hiAndrewQuinn]

More documentation updates.

The hard reflow default has been changed from Alt+Ctrl+Q to Ctrl+Shift+Q, so I put that change in.