fix Documentation of calculation of y_base

[Welthulk]

Fixes issue: # name and number of the issue

Changes proposed in this PR include:

Here you can elaborate on the chosen solution strategy, which changes did you make and which goal do they serve. Perhaps also which things are you still unsure of.

• ..

Could you please pay extra attention to the points below when reviewing the PR:

Here you can point out modules or complex implementation that require special attention, .e.g have a look at module foo.py and bar.py.

• ..

[mgovers]

Hi @sudo-ac and @Welthulk , can you please fix the DCO? You can follow the steps in https://github.com/PowerGridModel/power-grid-model/pull/496/checks?check_run_id=21620188944 .

[scud-soptim]

thx to all :-)