Mention that these are used for Android only

Change-Id: Ie9ae6c2087dd6757ca22eabe2073e1f03a5489c8

fontconfig/README

+This "bundled" fontconfig is built only in an Android build
+
 Fontconfig is a font configuration and customization library. It is designed to locate fonts
 within the system and select them according to requirements specified by applications. 
 

freetype/README

+This "bundled" freetype is built only in an Android build
+
 FreeType 2 is a software font engine that is designed to be small, efficient, highly customizable,
 and portable while capable of producing high-quality output (glyph images). It can be
 used in graphics libraries, display servers, font conversion tools, text image generation