Update README.rst

Author: tannewt

README.rst

@@ -60,7 +60,7 @@ To install in a virtual environment in your current project:
 
     mkdir project-name && cd project-name
     python3 -m venv .venv
-    source .env/bin/activate
+    source .venv/bin/activate
     pip3 install adafruit-circuitpython-usb-host-midi
 
 Installing to a Connected CircuitPython Device with Circup