gettext docs addition

[Marco van de Voort]

I was looking up the .po format, and noticed the question in this paragraph:

http://www.gnu.org/software/gettext/manual/gettext.html#object_002dpascal_002dformat

the answer is here:

http://www.freepascal.org/docs-html/rtl/sysutils/format.html

for ordinary strings and for datetime strings:

http://www.freepascal.org/docs-html/rtl/sysutils/formatchars.html

greetings

Marco