Update .gitignore when registering new files
Update .gitignore when registering new files

To reduce the risk of accidentally adding plaintext secrets, ignore
registered plaintext files.

ConnorAtherton/blackbox,wiredmax/blackbox,jasonchaffee/blackbox,unixorn/blackbox,sublimino/blackbox,StackExchange/blackbox,mavenlink/blackbox,Gnouc/blackbox,serialdoom/blackbox,quarkslab/blackbox,unixorn/blackbox,StackExchange/blackbox,ekristen/blackbox