fix[readme]: minor typos and formatting

[AdrianSkar]

Fix some typos, formatting and add an image for forked repos.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}