Add lino-framework/xl to requirements.txt
Add lino-framework/xl to requirements.txt

lsaffre/lino_book,lsaffre/lino_book,lino-framework/book,lino-framework/book,khchine5/book,lsaffre/lino_book,lino-framework/book,lino-framework/book,khchine5/book,khchine5/book