Feature request: confirm successful creation of encrypted message

After running `keybase encrypt -s user foo.txt` the program now exits without a message if the operation is successful. It would improve the UX if users saw confirmation that the operation succeeded and were also informed where the encrypted message resides (ie. `foo.txt.asc`)

Start by locating the CLI entry point that handles `keybase encrypt -s user foo.txt` and trace where the successful output file is chosen. Confirm the completed behavior reports success and identifies `foo.txt.asc`; add or update the relevant command test if one exists.

Written by the indexing model from the issue text.