Most documentation is in the fontanvil.pdf file in the doc/ subdirectory. 
From that file:

FontAnvil is a script language interpreter for manipulating fonts. 
FontAnvil is substantially compatible with the PfaEdit/FontForge native
scripting language, but FontAnvil is intended for non-interactive use; for
instance, invocation from the build systems of font packages like
Tsukurimashou.  To better serve font package build systems in general and
Tsukurimashou in particular, FontAnvil has no GUI and, to a reasonable
extent, avoids dependencies on external packages.

Flat text documents at the top level:
   AUTHORS   list of contributors inherited from FontForge
   COPYING   GNU GPL3 license applicable to the package as a whole, but
             read the important notices in fontanvil.pdf
   INSTALL   basic installation quick start instructions
   README    this file

FontAnvil is distributed by the Tsukurimashou Project at
   http://tsukurimashou.sourceforge.jp/

Matthew Skala
mskala@ansuz.sooke.bc.ca
http://ansuz.sooke.bc.ca/
