ZF-3650: Clarify standard PDF fonts limitations

Description

Standard PDF fonts support only Latin1 character set (actually some superset of Latin1 CS), even input string fro text drawing is represented in 'UTF-8' or any other encoding. Appropriate TTF fonts should be used for other character sets.

It should be described in the documentation.

Comments

Alex, can we fit this in to 1.7.1?

Done.