Minor README improvements for cross-platform install (#79)

Co-authored-by: Tyler Coles <tylercoles@gmail.com>

README.md

@@ -31,10 +31,12 @@ python3.11 -m venv .venv
 # activate it (after which `python` should be bound to the venv python)
 source .venv/bin/activate
 
-# then install the project in "editable" mode
-python -m pip install --editable .[dev]
+# then install the project in editable mode
+python -m pip install --editable ".[dev]"
 ```
 
+(The quotes in the last command are necessary on some platforms, but if the quotes give you issues you can also try without them.)
+
 ## Running from the command line
 
 The most basic task epymorph can perform is to run a spatial, compartmental disease simulation and output the time-series data of compartment populations (prevalence) as well as new events (incidence).