Add completion for commands and feeds

[ni3k]

Addresses issue #12

[h2337]

Thanks for taking time to contribute.

It doesn't work for me for some reason though, I built it and added few feeds, clicking tab after typing doesn't really do anything for me (I do have bash-completion installed).
Does it work for you?

[ni3k]

@jafarlihi you have to follow the steps for enabling autocompletion for the program when testing:

https://cli.urfave.org/v2/examples/bash-completions/

for me it was running the following command:

PROG=rssnix source ../cli/autocomplete/zsh_autocomplete

Edit: It seems I missed the enabling step, I'll add a commit addressing that

[ni3k]

@jafarlihi I added a setup command that enables autocompletion for zsh or bash profiles.
I tested it in following mode:

$ go install -a
$ rssnix s zsh
$ source ~/.zshrc
$ rssnix [Tab] ...