docs: Added instructions for running py interpreter in dev

py/README.md

@@ -32,3 +32,45 @@ serialized = """{"type": "Heading", "content": ["Heading Text"], "depth": 2}"""
 
 h2 = from_json(serialized)
 ```
+
+## Interpreter
+
+This library can also be used to interpret executable documents. Once installed it can be used like this:
+
+```bash
+$ python3 -m stencila.schema execute <inputfile> <outputfile> [parameters]
+```
+
+`inputfile` and/or `outputfile` can be set to `-` to read from stdin and/or write to stdout (respectively).
+
+`[parameters]` is a list of parameters to pass to the document –- these will differ based on what the document defines.
+They can be passed either by `--parameter_name=parameter_value` or `--parameter_name parameter_value`. Each parameter
+must be named.
+
+### Usage in Development
+
+There are three options to run the interpreter without installing this package (which can be useful when developing).
+
+#### setup.py develop
+
+Run `python3 setup.py develop` which will link this library into your site packages directory. You can then execute
+documents with the above Interpreter command.
+
+#### Run interpreter.py directly
+
+You can run the `interpreter.py` script directly, the arguments are the same as running as a module in the example
+above except the first `execute` argument is omitted:
+
+```bash
+$ python3 schema/py/stencila/schema/interpreter.py <inputfile> <outputfile> [parameters]
+```
+
+### cd into stencila directory
+
+You can run the interpreter as a module by changing into the `stencila` directory first, and then ommitting the
+`stencila` namespace:
+
+```bash
+$ cd schema/py/stencila
+$ python3 -m schema execute <inputfile> <outputfile> [parameters]
+```