Update INSTALL.txt
LB-773: Help should link to most up-to-date manual

Updated help link.
Merge remote-tracking branch 'sourcefabric/master' into devel
Merge pull request #48 from eozan/LB-773

LB-773: Help should link to most up-to-date manual
Merge branch 'devel' of https://github.com/sourcefabric/Ally-Py into devel