Allow user to upload file directly

[infogulch]

Hey there, cool project! I'm trying to use the docker version, but I'm having trouble actually mounting directories so they're readable.

My files are named like callgrind.benchmark_name.out so they don't match the default search pattern.

Also I tried mounting the directory docker run --rm -v ./:/tmp -p 8080:80 jokkedk/webgrind:latest but then it says "Webgrind $storageDir does not exist or is not writeable: /tmp/"

I renamed my files to match the pattern (cachegrind.out.benchmark_name) but that did not help either.

Instead of futzing with docker mounts or browsing files for a pattern that doesn't match, maybe it would be easier if users could just upload a file directly.

Looking closer, the repo only mentions cachegrind. Can webgrind interpret callgrind.out files as well?