install docs: don't use "from" twice
install docs: don't use "from" twice

it always abstracts "pypi" and "github" away (technical words that are
not necessary). pip remains.

raxenak/borg,edgimar/borg,edgimar/borg,RonnyPfannschmidt/borg,raxenak/borg,edgimar/borg,edgewood/borg,edgimar/borg,edgewood/borg,RonnyPfannschmidt/borg,raxenak/borg,mhubig/borg,RonnyPfannschmidt/borg,edgewood/borg,mhubig/borg,mhubig/borg,edgewood/borg,RonnyPfannschmidt/borg,RonnyPfannschmidt/borg,raxenak/borg