add a faq entry for a message outdated pip/setuptools can output (#3971)
* add a faq entry for a message outdated pip/setuptools can output
* attention to detail is not my strong suit
diff --git a/docs/faq.rst b/docs/faq.rst
index 7133f0c..4ab518e 100644
--- a/docs/faq.rst
+++ b/docs/faq.rst
@@ -84,6 +84,13 @@
newer ``gcc`` and then install ``cryptography`` using
``CC=/path/to/newer/gcc pip install cryptography``.
+Installing ``cryptography`` fails with ``Invalid environment marker: python_version < '3'``
+-------------------------------------------------------------------------------------------
+
+Your ``pip`` and/or ``setuptools`` are outdated. Please upgrade to the latest
+versions with ``pip install -U pip setuptools`` (or on Windows
+``python -m pip install -U pip setuptools``).
+
Installing cryptography with OpenSSL 0.9.8 or 1.0.0 fails
---------------------------------------------------------