Improve order_gfa documentation

[adadiehl]

Please add complete description of output files and their content. In particular, please explain the meaning and interpretation of B0 and N0 tags relative to the following excerpt:

"...bubbles in the graphs are identified using gaftools (commit ID: 919bbec).
The function order_gfa tags the nodes of the graph to identify whether the nodes are bubble nodes (nodes inside a bubble) or scaffold nodes (nodes outside a bubble)."

(https://www.biorxiv.org/content/10.1101/2024.04.18.590093v1.full.pdf)

[fawaz-dabbaghieh]

Thank you for your comment, Adam.
Indeed, we need to add more documentation which we are working on. In the meantime, I wrote this quick explanation on the order_gfa subcommand, I hope it helps here.

[adadiehl]

Thank you, this is very helpful!