Merge pull request #94 from rhoerbe/master

Added note on dependency for centos install

Author: Roland Hedberg

doc/install.rst

@@ -42,6 +42,10 @@ Once you have installed all the necessary prerequisites a simple::
 
 will install the basic code.
 
+Note for rhel/centos 6: cffi depends on libffi-devel, and cryptography on openssl-devel to compile
+So you might want first to do:
+yum install libffi-devel openssl-devel
+
 After this you ought to be able to run the tests without an hitch.
 The tests are based on the pypy test environment, so::