README: Update for modffi being enabled by default for unix port.

README.md

@@ -55,7 +55,8 @@ Then to test it:
 
 Debian/Ubuntu/Mint derivative Linux distros will require build-essentials and
 libreadline-dev packages installed. To build FFI (Foreign Function Interface)
-module (recommended, enable in unix/mpconfigport.mk), libffi-dev is required.
+module, libffi-dev package is required. If you have problems with some
+dependencies, they can be disabled in unix/mpconfigport.mk .
 
 The STM version
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