What would you like to be added:
I would like stern to have the ability to parse logs from stdin.

Why is this needed:
Sometimes logs are stored on file and I find it inconvenient to use a second tool to print the log file. For me, this is mainly a problem because the templates I use with stern are bothersome to translate to another tool if it's at all possible.

I've been working on some changes for this so I'll open a PR soon.