CONFIG_KEEP_MONTHS should be better documented

[mdzio]

The documentation should be extended:
By setting the environment variable CONFIG_KEEP_MONTHS, maintenance is performed before the CCU-Historian is actually started. One after the other the CCU-Historian is called with the options -clean, -recalc and -compact.

See also: Comment on CCU-Historian Issue

[jokay]

Good point, information added.