DOC: (Hopefully) small clarification to plot_evoked_topomap() docstring (#7554)
DOC: (Hopefully) small clarification to plot_evoked_topomap() docstring (#7554)

* DOC: (Hopefully) small clarification

I slightly changed the docstring of the vmin and vmax parameters,
and hope it's easier to understand now.

* DOC: Implement @drammock's suggestion

* Fix ref
mne-tools/mne-python,olafhauk/mne-python,kingjr/mne-python,cjayb/mne-python,wmvanvliet/mne-python,kambysese/mne-python,larsoner/mne-python,olafhauk/mne-python,kingjr/mne-python,kambysese/mne-python,larsoner/mne-python,olafhauk/mne-python,wmvanvliet/mne-python,drammock/mne-python,Teekuningas/mne-python,Eric89GXL/mne-python,Eric89GXL/mne-python,cjayb/mne-python,bloyl/mne-python,rkmaddox/mne-python,wmvanvliet/mne-python,kingjr/mne-python,larsoner/mne-python,Teekuningas/mne-python,pravsripad/mne-python,drammock/mne-python,bloyl/mne-python,Teekuningas/mne-python,drammock/mne-python,mne-tools/mne-python,rkmaddox/mne-python,mne-tools/mne-python,pravsripad/mne-python,pravsripad/mne-python