docs: add details to interactive mode in manpage (closes #805)

[LoricAndre]

Checklist

check the box if it is not applicable to your changes

• I have updated the README with the necessary documentation
• I have added unit tests
• I have added end-to-end tests
• I have linked all related issues or PRs

Description of the changes

[LoricAndre]

@not-my-profile could you take a look at this and tell me if it seems good to you ? Please tell me if anything is still unclear to you, this part of the documentation is really lacking at the moment and this is a good opportunity to better it.

[not-my-profile]

It's still not clear to me why -i and -c are separate and also what happens when you do -i without -c.

[LoricAndre]

How is this ?

[not-my-profile]

I think all the available modes should be explained at the top of the man page after:

sk is a general purpose command-line fuzzy finder.

and before the ENVIRONMENT VARIABLES. Then the CLI flags can refer to that explanation.

And there it would be important to mention what the default mode is.

[LoricAndre]

That's a good idea ! Please take a look when you can and tell me what you think.

[not-my-profile]

Btw I think you have to move the "closes #805" into the commit message body, I don't think GitHub recognizes it in the title.