[Feature] --insert flag

[gedw99]

Is your feature request related to a problem? Please describe.

The none golang version has the ability to insert the generated TOC into the markdown file.

It would be nice if the golang tool also did that.

Describe the solution you'd like

A clear and concise description of what you want to happen.

Like so:

gh-md-toc --insert examples/02/README.md
gh-md-toc: error: unknown long flag '--insert', try --help

Describe alternatives you've considered

I could do it manually but well i am hoping this is something everyone might need.

Additional context

[ekalinin]

Hey,

Thanks for the report. It looks like we already have such an issue - #26