Doc fixes the prequel

[StanczakDominik]

A smaller and leaner prequel to #1073

[codecov]

Codecov Report

Merging #1076 (b9e47cf) into master (af07d43) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1076   +/-   ##
=======================================
  Coverage   96.91%   96.91%           
=======================================
  Files          70       70           
  Lines        6929     6929           
=======================================
  Hits         6715     6715           
  Misses        214      214           

Impacted Files	Coverage Δ
plasmapy/optional_deps.py	100.00% <ø> (ø)
plasmapy/plasma/exceptions.py	100.00% <ø> (ø)
plasmapy/plasma/sources/openpmd_hdf5.py	80.00% <ø> (ø)
plasmapy/plasma/sources/plasma3d.py	100.00% <ø> (ø)
plasmapy/plasma/sources/plasmablob.py	100.00% <ø> (ø)
plasmapy/simulation/abstractions.py	76.04% <ø> (ø)
plasmapy/simulation/particle_integrators.py	100.00% <ø> (ø)
plasmapy/simulation/particletracker.py	98.27% <ø> (ø)
plasmapy/utils/code_repr.py	100.00% <ø> (ø)
plasmapy/utils/datatype_factory_base.py	100.00% <ø> (ø)
... and 1 more

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[StanczakDominik]

I'll be merging this in a few hours, before the release, if nobody objects :)