docs: rewrite pip/source install section
docs: rewrite pip/source install section

gravyboat/streamlink,streamlink/streamlink,chhe/streamlink,chhe/streamlink,streamlink/streamlink,melmorabity/streamlink,beardypig/streamlink,bastimeyer/streamlink,beardypig/streamlink,melmorabity/streamlink,gravyboat/streamlink,bastimeyer/streamlink