Updating locales is busted after missing README got added to translation repo in c2f257dd3d3b9a3bee707b2743fffeea4751476a

Our Makefile for generating the check.tpo locales does not cope well with (randomly) added files. As a README file got added to the translation repo we have to adjust our Makefile to exclude that one during our locale generation or otherwise it fails.

/cc @emmapeel