Update readme

Author: samwillis

README.pypi.md

@@ -5,6 +5,8 @@ Node.js PyPI distribution
 
 The [node-js][pypi] Python package redistributes Node.js so that it can be used as a dependency of Python projects.
 
+**This is intended for use within Python virtual environments and containers, it should not be used for global instillation.**
+
 [zig]: https://nodejs.org/
 [pypi]: https://pypi.org/project/node-js/
 
@@ -17,14 +19,33 @@ To run the Zig toolchain from the command line, use:
 python -m nodejs
 ```
 
-To run Node.js from a Python program, use `sys.executable` to locate the Python binary to invoke. For example:
+`npm` and `npx` are also available as `python -m nodejs.npm` and `python -m nodejs.npx`.
+
+To run Node.js from a Python program:
+
+```python
+from nodejs import node, npm, npm
+
+# Run Node.js and return the exit code.
+node.run(['script.js', 'arg1', ...])
+
+# Run npm and return the exit code.
+npm.run(['command', 'arg1', ...])
+
+# Run npx and return the exit code.
+npx.run(['command', 'arg1', ...])
+```
+
+Alternatively use `sys.executable` to locate the Python binary to invoke. For example:
 
 ```python
 import sys, subprocess
 
 subprocess.call([sys.executable, "-m", "nodejs"])
 ```
 
+`node`, `npm` and `npx` are also added to your Python environment's `bin` directory. This is usually on your `PATH` and so they should be available in your shell environment.
+
 License
 -------