Clarified doc .bashrc config

research/object_detection/g3doc/installation.md

@@ -91,7 +91,8 @@ export PYTHONPATH=$PYTHONPATH:`pwd`:`pwd`/slim
 
 Note: This command needs to run from every new terminal you start. If you wish
 to avoid running this manually, you can add it as a new line to the end of your
-~/.bashrc file.
+~/.bashrc file, replacing \`pwd\` with the absolute path of
+tensorflow/models/research on your system.
 
 # Testing the Installation