Add pdfpc files to Tex.gitignore

The presentation software pdfpc [1] (which is handy for latex beamer slides) supports additional notes on the secondary screen provided by *.pdfpc files.
These can be autogenerated from latex documents with the pdfpcnotes package [2], thus should be ignored in a latex project (but not in others where they could have been created manually).

[1] https://pdfpc.github.io/
[2] https://github.com/cebe/pdfpc-latex-notes