LAVA-1167 document the 'history' feature
LAVA-1167 document the 'history' feature

This allow to remove .git directory from the overlay.

Change-Id: I655124cd468e76444ffef24216eb06c1b2ebb4ee

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server