Add documentation for Case[sauf2] feature

[diegoluinetti]

This document details the inflectional feature 'Case[sauf2]' in Old Georgian, explaining its structure and usage across various grammatical categories. for UD_Old_Georgian-LauRo

[dan-zeman]

Warning: I am not sure that we ever had a layered feature with a digit in the layer label, and more importantly, that all pieces of our infrastructure will digest it. (I am not saying that it is illegal; it is not.)

[diegoluinetti]

In the naming of this feature we followed the already existing Case[stack2].md in docs/_oge/feat

[dan-zeman]

In the naming of this feature we followed the already existing Case[stack2].md in docs/_oge/feat

Understood. But that's exactly the one which alerted me to the problem we may have here. Currently it is reported as an error at https://quest.ms.mff.cuni.cz/udvalidator/cgi-bin/unidep/langspec/specify_feature.pl?lcode=oge, so I suppose it will not work if used in the data.

[diegoluinetti]

Case[sauf2] changed to Case[dsauf]