Move the data-prep docs over from higlass

[mccalluc]

Description

What was changed in this pull request?

• Copy docs from higlass

Complements higlass/higlass#628 (deletion of same file in the higlass repo); Toward #66 ... but I'm not sure that a sphinx build is worth the effort. I think it would be good to reorganize this document, though. Currently, a single page, with these headings:

   Bed Files
   Bedpe-like Files
   BedGraph files
   bigWig files
   Chromosome Sizes
   Gene Annotation Tracks
   Hitile files
   Cooler files
   Multivec Files
   Epilogos Data (multivec)
   States Data (multivec)
   Other Data (multivec)

I would propose to split it up like this, with each getting its own page. It's dense currently, and my guess is that users come to this with one kind of data at a time, and would prefer a smaller page with just the data they need:

   Non-genomic raster data
   Genomic data
      Bed Files
      Bedpe-like Files
      BedGraph files
      bigWig files
      Chromosome Sizes
      Gene Annotation Tracks
      Hitile files
      Cooler files
      Multivec Files (Maybe multivec is a single page?)
         Epilogos Data (multivec)
         States Data (multivec)
         Other Data (multivec)

Checklist

• Unit tests added or updated
• Updated CHANGELOG.md

[pkerpedjiev]

I would propose to split it up like this, with each getting its own page. It's dense currently, and my guess is that users come to this with one kind of data at a time, and would prefer a smaller page with just the data they need:

That's a good idea. This PR or another one? I'm going to approve this PR, if you want to include the reorganization, that's fine. If you want to squash and merge and create a new PR for the reorganization that's fine too.

[mccalluc]

I'll go ahead and merge this now, so higlass/higlass#628 can also be merged, and probably have PR for the doc reorg later today. Thanks!