ParseDb doc clarity issues

[Jason Vander Heiden]

In the C-primer/alignment disagreement section it's not clear that the example will not work with the Jiang et al, S43 example file. We just need to either upload valid example data for that task or make clear that db.tab is not a real file.

Probably the same for other instances of db.tab.

[Namita Gupta]

Clarified that db.tab is imaginary for now in b818db4