Update --debug to state if it's using stdin or the file system

[JohnC32]

Please update --debug switch to indicate if ripgrep is searching stdin or a file system directory (and print which one).

Rationale:

I used ripgrep from within a Makefile and in a terminal, it worked fine. However, when I used it from within Emacs via M-x compile RET make RET ripgrep returned no results. Reading the help, led me to add --debug, but it didn't say why ripgrep wasn't working as I expected.

After a bit of debugging I found that ripgrep reads stdin (emacs sets this up) which caused ripgrep to behave differently when running GNU make from within Emacs. I later saw in the doc that this is intended behavior, so no issue with that. Having --debug explain what is going on would have saved me a bit of debugging.

Thanks