Document incompatibilities between bst releases

bst 1.0 -> 1.2:

Config file default to not push to cache servers, you have tu specify "push: true" (See #224 (closed))
cache-key has been changed (See #326 (closed))
changes in the default value of build-root (See #414 (closed))
ostree-based cache server is gone

bst 1.2 -> 1.4:

Edited Sep 20, 2018 by Javier Jardón

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information