- Add a tab completion script for bash.
pg-psql -> psql

Fixes #67.
Remove `godep go get` command from instructions

This subcommand appears to have been deprecated, and doesn't seem to be
required to get `hk` to build:

```
Any go tool command can run this way, but "godep go get"
is unnecessary and has been disabled. Instead, use
"godep go install".
```