Documentation: update jupyterlab requirements for linked jupytext not…

[nthiery]

Reference: jupyterlab/jupyterlab#13743

[mwouts]

Thank you @nthiery for making this possible!

By the way, what would you think of simplifying "jupyterlab>=3.6.0 or jupyterlab>=4.0.0a16" into just "jupyterlab>=3.6.0" in this PR?

[nthiery]

Yeah, I pondered about it; the double formulation is indeed confusing if the reader
does not have in mind that there are two distinct lines and versions don't form a
total order.

The simplified formulation >= 3.6 is making an assumption: that the user is not
using a quite old jupyterlab 4 prerelease. Presumably it is fine to make
this assumption, taking for granted that a someone using such an old
prerelease must be a power user with very specific needs that will know
what they are doing.

[mwouts]

Yea exactly! I think it has been a while since that feature is available in the version 4dev, so this should be a safe assumption in practice 😀