diff --git a/docs/development/getting-started.rst b/docs/development/getting-started.rst
index 953ae95..e01ee27 100644
--- a/docs/development/getting-started.rst
+++ b/docs/development/getting-started.rst
@@ -19,6 +19,10 @@
     $ pip install --requirement dev-requirements.txt
     $ pip install --editable .
 
+Make sure that ``pip install --requirement ...`` has installed the Python
+package ``vectors/`` and packages on ``tests/`` . If it didn't, you may
+install them manually by using ``pip`` on each directory.
+
 You will also need to install ``enchant`` using your system's package manager
 to check spelling in the documentation.