Improve README

[osulli]

What

Improves readme with the following:

• Fixes missing backslash in example
• Makes assumptions easier to read
• Restructures into a much more readable format
• Makes shell examples easier to copy and paste into the terminal
• Fixes typos and bad grammar
• Makes usage (jump-host) and lack of user management a lot clearer
• Clearer / More Consistent headers under Usage section

... generally makes the document much more linear and easier to follow as a new-user.

[tamsky]

LGTM

[osulli]

@tamsky able to put that LGTM as a review pls?