docs(python): Add additional python_binary example (#2728)

Have added an additional example for the `python_binary` option to show
how to display the version of python from inside a local virtual
environment.

docs/config/README.md

@@ -2274,6 +2274,17 @@ python_binary = "python3"
 detect_extensions = []
 ```
 
+```toml
+# ~/.config/starship.toml
+
+[python]
+# Display the version of python from inside a local venv.
+#
+# Note this will only work when the venv is inside the project and it will only
+# work in the directory that contains the venv dir but maybe this is ok?
+python_binary = ["./venv/bin/python", "python", "python3", "python2"]
+```
+
 ## Red
 
 By default the `red` module shows the currently installed version of [Red](https://www.red-lang.org/).