Update README.md according to style
Update README.md according to style

Previously, the README.md file was updated but didn't match existing
Github style. This commit wraps near 80 columns (markdown links make
that a bit harder) and eliminate unnecessary steps (linking to
existing documentation and removing redundant declarations).

urimikhli/myboxen,tarVolcano/my-boxen,mnussbaum/my_boxen,mnussbaum/my_boxen,urimikhli/myboxen,tarVolcano/my-boxen,tarVolcano/my-boxen,urimikhli/myboxen,mnussbaum/my_boxen