Add the ability to specify a flag that will automatically choose the selected repository upon opening

[Cody Mikol]

To be able to use this in an effective way with my other projects, I'd like to be able to add some flags to auto open a directory

./gradlew run --directory ~/dev/src/foo

utltimately I'd add an alias / macro for this then so I can just hit g to open the current directory in gitdown