Get txt output instead of xml

The xml format adds token count with the tags.

Also the xml format does not open properly in two common web browsers I tested.

And an option to generate the .txt would be good.

The XML format is much harder to read and navigate in plaintext when the user's desire is to trim down the repomix output without having to duplicate and delete items in their codebase before running repomix.

It would also be well if there was 'npx repomix help' option so the user can have these commands presented to them (generate txt with 'npx repomix txt' etcetera for any other help info.)

-T