Updated README.md
Updated README.md

Updated README.md for easier navigation and discovery of installation
methods.

bastimeyer/streamlink,javiercantero/streamlink,javiercantero/streamlink,bastimeyer/streamlink,wlerin/streamlink,streamlink/streamlink,melmorabity/streamlink,gravyboat/streamlink,beardypig/streamlink,ethanhlc/streamlink,melmorabity/streamlink,chhe/streamlink,mmetak/streamlink,ethanhlc/streamlink,mmetak/streamlink,beardypig/streamlink,wlerin/streamlink,fishscene/streamlink,chhe/streamlink,streamlink/streamlink,back-to/streamlink,gravyboat/streamlink,back-to/streamlink,fishscene/streamlink