Add a note about the PDF display problem
Add a note about the PDF display problem

when producing the documentation as a PDF the unicode braille is not
displayed.

liblouis/liblouis,BueVest/liblouis,liblouis/liblouis,IndexBraille/liblouis,BueVest/liblouis,liblouis/liblouis,BueVest/liblouis,IndexBraille/liblouis,hammera/liblouis,vsmontalvao/liblouis,vsmontalvao/liblouis,hammera/liblouis,liblouis/liblouis,vsmontalvao/liblouis,BueVest/liblouis,IndexBraille/liblouis,liblouis/liblouis,vsmontalvao/liblouis,IndexBraille/liblouis,BueVest/liblouis,IndexBraille/liblouis,hammera/liblouis,liblouis/liblouis,hammera/liblouis,hammera/liblouis,hammera/liblouis,BueVest/liblouis,vsmontalvao/liblouis