blackbox: Update README, add --homedir to encryption step in _blackbox_common
blackbox: Removed homedir and updated README to add step to import pubring
blackbox: Removed the manual gpg --import step from README, added prepare_keychain to blackbox_update_all_files
Merge pull request #20 from loadstar81/master

Add a call to prepare_keychain in blackbox_update_all_files