Update extending FAQ for Python 3

Author: hugovk

Doc/faq/extending.rst

@@ -246,13 +246,12 @@ Then, when you run GDB:
 I want to compile a Python module on my Linux system, but some files are missing. Why?
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-Most packaged versions of Python don't include the
-:file:`/usr/lib/python2.{x}/config/` directory, which contains various files
+Most packaged versions of Python don't include some files
 required for compiling Python extensions.
 
-For Red Hat, install the python-devel RPM to get the necessary files.
+For Red Hat, install the python3-devel RPM to get the necessary files.
 
-For Debian, run ``apt-get install python-dev``.
+For Debian, run ``apt-get install python3-dev``.
 
 How do I tell "incomplete input" from "invalid input"?
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