Docs update

docs/source/adding-mutant-generation.rst

@@ -1,2 +1,26 @@
 Adding a Mutant Generation Approach
 ===================================
+
+To add a mutant generation approach to *multiplex*, users should create a package for their approach in the ``multiplex/approach/`` directory.
+
+Users can copy the ``basic`` example to get started and then build their own approach using the underlying setup.
+
+Each approach has a ``controller.py`` file that is called by ``multiplex/__main__.py``.
+Currently users must add their approach call to ``__main__.py`` following the template of the existing approaches. 
+
+.. code-block:: Python
+
+   """Controller for Basic prompt approach."""
+
+   from approach.basic.code_generator import generate_code
+
+
+   def main(model, output_dir, prompts, language):
+       """Controller for Basic prompt approach"""
+
+       generate_code(model, output_dir, prompts["basic_generate_mutants"], language)
+
+
+   def __main__(model, output_dir, prompts, language):
+       main(model, output_dir, prompts, language) 
+