Auto-indexing: support relative paths

[keynmol]

In Maven you can point to a relative path to search for pom file.

If the relative path doesn't exist (i.e. you mount only a subfolder of the tree), we fail.

It'd be good to support --work-dir argument so that the indexer works from that root, no matter where it's launched from

[keynmol]

We have --cwd parameter which supports that, just need to be documented (I believe it's provided by Moped implicitly?)