Added a note about there being no guarantee of stability of the Python C ABI between Python versions and how this can cause trouble with CFFI.

Author: tleonhardt

cffi/Readme.md

@@ -18,3 +18,13 @@ Compare the results of a pure Python implementation to that of the CFFI wrapper
     * fibonacci.h/.c
 * CFFI "wrapper" (there is no wrapper code, its all inline Python)
     * test_cffi.py
+    
+    
+## Troubleshooting
+The ABI of the C API is generally not stable and may change between versions of Python. This can 
+cause code which used to work to break when you upgrade either your version of Python or CFFI.
+ 
+If you get a Python traceback from an exception that contains something like "ImportError: dlopen", 
+then you may have a mismatch between your version of Python and your version of CFFI.  Try upgrading
+one or both.  The **conda** package manager which ships with the Anaconda Python distro is convenient
+for this.