Add package dependency to docs

Build from sources now requires python-pyftpdlib
which is in repo, but not mentioned in docs

Signed-off-by: Mick Grant <arceye@mgware.co.uk>
Merge pull request #33 from ArcEye/master

Add package dependency to docs
another apt-get update is needed to refresh the key
Merge pull request #34 from strahlex/apt-get-fix

another apt-get update is needed to refresh the key
added additional update to accept key and fixed tab intendation
Merge pull request #35 from strahlex/update-fix

added additional update to accept key and fixed tab intendation