Add documentation to the low-level `Pp` functions.
Add documentation to the low-level `Pp` functions.

Thanks to HH for pointing it out.

JasonGross/coq,Zimmi48/coq,coq/coq,ppedrot/coq,JasonGross/coq,maximedenes/coq,gares/coq,SkySkimmer/coq,Lionel-Rieg/coq,mattam82/coq,Matafou/coq,amintimany/coq,Matafou/coq,Ptival/coq,ejgallego/coq,gares/coq,Zimmi48/coq,mattam82/coq,maximedenes/coq,gares/coq,gares/coq,gares/coq,amintimany/coq,Zimmi48/coq,SkySkimmer/coq,coq/coq,william-lawvere/coq,letouzey/coq-wip,letouzey/coq-wip,william-lawvere/coq,ejgallego/coq,letouzey/coq-wip,SkySkimmer/coq,Ptival/coq,coq/coq,mattam82/coq,ppedrot/coq,ppedrot/coq,ejgallego/coq,Ptival/coq,coq/coq,ppedrot/coq,maximedenes/coq,maximedenes/coq,JasonGross/coq,ejgallego/coq,SkySkimmer/coq,letouzey/coq-wip,letouzey/coq-wip,ppedrot/coq,amintimany/coq,Matafou/coq,silene/coq,maximedenes/coq,silene/coq,silene/coq,Lionel-Rieg/coq,JasonGross/coq,william-lawvere/coq,Zimmi48/coq,Lionel-Rieg/coq