docs: document the fix for incompatible pip-tools with newer pip

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/docs/INSTALL.rst b/docs/INSTALL.rst
index 63c9369c67f1a057f210943a0f3230f183b19f42..2af50af8eb522e423de3dedce594b0b9a1ee15f4 100644 (file)
--- a/docs/INSTALL.rst
+++ b/docs/INSTALL.rst
@@ -70,3 +70,16 @@ and should work with teuthology. But if you want to bump up the versions of them
 please use the following command to update this file ::
 
   pip-compile -qo- | sed '/^-e / d' > requirements.txt
+
+Please upgrade pip-tool using following command ::
+
+  pip install pip-tools --upgrade
+
+if the command above fails like::
+
+  Traceback (most recent call last):
+  File "/home/kchai/teuthology/virtualenv/bin/pip-compile", line 5, in <module>
+    from piptools.scripts.compile import cli
+  File "/home/kchai/teuthology/virtualenv/local/lib/python2.7/site-packages/piptools/scripts/compile.py", line 11, in <module>
+    from pip.req import InstallRequirement, parse_requirements
+  ImportError: No module named req