add indent to requirements

Without indent, `make` reports errors in somewhere in a directory called codelets.  
It also reports "/bin/bash: indent: command not found" not far away.

For my Ubuntu 14.04 flavor, a simple `sudo apt-get install indent` made `make` work as expected.

README

@@ -26,7 +26,7 @@ If you have downloaded an official release, please read chapter
      make install
 
 If you are using the git repository, install ocaml, autoconf,
-automake, and libtool, and execute the bootstrap.sh script.  Most of
+automake, indent and libtool, and execute the bootstrap.sh script.  Most of
 the source code of fftw is generated automatically, and this script
 generates all the required source files.