Improve advection docstring

[Z-Richard]

Description Of Changes

Improves the documentation of mpcalc.advection.

Checklist

• Closes Clean up advection docs #2678

[dopplershift]

Thanks for the contribution! Just a couple minor tweaks and (provided Sphinx is happy) this is good to go!

[dopplershift]

Would you be wiling to add a Notes section with the equation for advection, similar to what's in vorticity:

MetPy/src/metpy/calc/kinematics.py

Lines 75 to 88 in ae58134

	Notes
	-----
	This implements a numerical version of the typical vertical vorticity equation:
	.. math:: \zeta = \frac{\partial v}{\partial x} - \frac{\partial u}{\partial y}
	If sufficient grid projection information is provided, these partial derivatives are
	taken from the projection-correct derivative matrix of the vector wind. Otherwise, they
	are evaluated as scalar derivatives on a Cartesian grid.
	.. versionchanged:: 1.0
	Changed signature from ``(u, v, dx, dy)``
	"""

?

[Z-Richard]

Yes, I added an equation to the Notes section. Now that the PR passes all the tests, it should be good to go in.

[dopplershift]

Looks good to me!