FIXUP P1868R2: reword reference as suggested by Hubert in #3753

Author: Dawn Perchik

source/intro.tex

@@ -60,9 +60,9 @@
 \item ISO 80000-2:2009, \doccite{Quantities and units ---
 Part 2: Mathematical signs and symbols
 to be used in the natural sciences and technology}
-\item Unicode Standard Annex, UAX \#29, \doccite{Unicode Text Segmentations},
-version 12.1.0.
-Available at \url{http://www.unicode.org/reports/tr29/tr29-35.html}
+\item The Unicode Consortium. Unicode Standard Annex, UAX \#29, \doccite{Unicode Text Segmentation} [online].
+Edited by Mark Davis. Revision 35. 2019-02-15 [viewed 2020-02-23].
+Available from: \url{http://www.unicode.org/reports/tr29/tr29-35.html}
 \end{itemize}
 
 \pnum