Thank you @augusto-herrmann . Sure we should add something along these lines. Also, I may move that comment upwards as actually it is common to both Jupyter notebook and Jupyter Lab.

Codecov Report

Merging #304 into master will decrease coverage by 1.26%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #304      +/-   ##
==========================================
- Coverage    99.2%   97.94%   -1.27%     
==========================================
  Files          70       70              
  Lines        6701     6533     -168     
==========================================
- Hits         6648     6399     -249     
- Misses         53      134      +81

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@augusto-herrmann I am sorry I can't find the time for merging this - do you mind if I do that in a few weeks time? I think it's worth mentioning the server extension but in most configurations the user does not need to know about it: it's on by default, and all it does it to switch the contents manager to Jupytext's one, which can also be achieved manually following the intruction after

If you don't have the notebook icon on text documents after a fresh restart of your Jupyter server, install the contents manager manually

Sure, I don't mind it at all! :)
I'm just trying to help with the documentation a bit.