update Midpoint doc.

midpoint/rtr-midpoint.md

@@ -115,11 +115,18 @@ git clone http://git.abbether.net/return-to-ritherdon/midpoint.git
 cd midpoint
 ```
 
-From there, you will need to create a Python virtual environment,
+From there, you can create a Python virtual environment if you prefer
+to keep things isolated. You can ignore the virtual environment step
+and install the requirements at a system-wide level. If you do that,
+you will need to use `pip3` instead of `pip`.
 
 ```bash
 # Adjust the path to suit to environment.
 python3 -m venv ~/repos/midpoint/venv
+
+# Install the requirements...
+(use pip3 if you're not using a virtual environment)
+pip install -r requirements.txt
 ```
 
 As an aside, I created a virtual environment with `python3 -m venv