Doc: NR 1.8.2 - add \abs-fontsize to main doc (issue 5969060)

[tdanielsmusic]

LGTM, apart from the one change suggested.

Trevor


http://codereview.appspot.com/5969060/diff/2001/Documentation/notation/text.itely
File Documentation/notation/text.itely (right):

http://codereview.appspot.com/5969060/diff/2001/Documentation/notation/text.itely#newcode544
Documentation/notation/text.itely:544: It can be set to a fixed value,
Better to re-emphasize this is _relative_ to the value set by the global
staff size, perhaps by saying, "It can be increased or decreased
relative to the value set by the global staff size,"  Maybe include
\fontsize #-2 in the example below to show sizes smaller than that set
by the global staff size can be specified.

http://codereview.appspot.com/5969060/