update FAQ for past.builtins

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
diff --git a/FAQ.txt b/FAQ.txt
index cc61eff..b62487c 100644
--- a/FAQ.txt
+++ b/FAQ.txt
@@ -34,3 +34,7 @@
       make install
       make modules_install
       make headers_install INSTALL_HDR_PATH=/usr/local/
+
+Q: hello_world.py fails with:
+   ImportError: No module named past.builtins
+A: sudo pip install future