[Feature request]: Add option to add and remove subscriptions

[n8x0b7T]

Background

• [x] I have checked ytfzf(1) and ytfzf(5) or the wiki before creating this.

Problem

Adding a feature to manage subscriptions would complement the existing subscription feed.

Feature

Given a channel id or a channel name, this option could add or remove an item in the ~/.config/ytfz/subscriptions file.

[Euro20179]

I don't see the need as you can really just write a basic wrapper script, or even just run ytfzf --channel-link="some-channel-link" >> $HOME/.config/ytfzf/subscriptions in a terminal.

However, this is an excellent extension idea that I'll try writing.