Catalyst Game Labs has released a Battletech Primer for those new to the game and the following link to a page.
"Initially published over thirty years ago as a tabletop board game, BattleTech has gone on to become one of the gaming industry’s most important and longest-lasting science-fiction universes. In the free
pdf
BattleTech Primer(62.05 MB)
PDF above (it’s 65 megs, so may load slow depending upon your internet connection) we will explore a little of the property’s history of products and skim the surface of BattleTech’s incredibly rich fictional setting."