README: Fix pip install command

The pip install command accidentally had `-m` when `-e` was intended.
Also quote the argument for maximum shell compatibility

Signed-off-by: Joshua Watt <[email protected]>

README.md

@@ -323,7 +323,7 @@ python3 -m venv .venv
 Next install the project in editable mode with development dependencies:
 
 ```bash
-pip install -m .[dev]
+pip install -e '.[dev]'
 ```
 
 Finally, to run tests use `unittest`: