Data model for the emline files

[araichoor]

This PR updates the two datamodel *.rst files for the emline files.
The description is done in emline-SPECTROGRAPH-TILEID-GROUPID.rst, to which refers emline-SURVEY-PROGRAM-PIXNUM.rst.

I know the test will fail with being unhappy with the 1e-17 erg/s/cm^2-like units; though I don't know what is the correct approach here, so I'd appreciate guidelines.

Thanks!

[weaverba137]

Units need to be fixed up, but otherwise this looks fine.

[weaverba137]

@araichoor, I can patch up these units issues in order to get this merged quickly. However, I noticed a significant discrepancy, even after getting the units into a standard form:

OII_FLUX          float32 1e-17 erg/s/cm^2                Fitted flux for the OII doublet
OII_FLUX_IVAR     float32 1e34 / erg^2 * s^2 * cm^4 * A^2 Inverse variance of the fitted flux for the OII doublet

The inverse variance had inconsistent units relative to OII_FLUX. There are several columns where this is the case.

[moustakas]

Also, in the explanation / documentation column: OII --> [OII]

[araichoor]

Thanks a lot @weaverba137 for the comments/help (and @moustakas also).
I've made the changes (correct units, remove blank lines in the notes and examples, and add brackets around OII and OIII).
A built documentation is here: https://data.desi.lbl.gov/desi/users/raichoor/tmpdir/desidatamodel_emline/20220613-v0/html/DESI_SPECTRO_REDUX/SPECPROD/tiles/GROUPTYPE/TILEID/GROUPID/emline-SPECTROGRAPH-TILEID-GROUPID.html

Please let me know if there are other things to change.

[weaverba137]

@araichoor, thank you this looks fine. I'm going to go ahead and merge.

[coveralls]

Coverage remained the same at 100.0% when pulling 6e3d64b on emline into e1204fe on main.