Updated Structure of the code (markdown)

Structure-of-the-code.md

@@ -42,11 +42,12 @@ Broadly, osxphotos works like this:
 As an example, here's a rough outline of what you'd need to do to add support for a new metadata attribute:
 1. Reverse engineer Photos.sqlite and develop an sql query that extracts the data
 2. Add this query to `PhotosDB._process_database5` (assuming a Photos 5 library) and store the data in appropriate data structure accessible through `_dbphotos`
-3. Add a property to `PhotoInfo` which accesses `_dbphotos` through `self._db` which points to the PhotosDB object
+3. Add a property to `PhotoInfo` which accesses `_dbphotos` through `self._db` which points to the PhotosDB object.  If your change requires significant code, consider creating a separate file for the method -- see _photoinfo_export.py for an example
 4. If exposing the property to the templating system (`PhotoInfo.render_template()`) and add it to `templates.py` (which is relatively self-documenting)
 5. If exposing the property to the command line interface, add it to `__main__.py` -- you'll want to look at `query_options`, `_query()`, `export()`, and `export_photo()` at a minimum to ensure the command line tool can access your new attribute. 
 6. Add at least one test to `tests/`!
 7. Ensure all tests pass `python3 -m pytest tests/`
-8. Submit a pull request :-)
+8. Format code with [black](https://black.readthedocs.io/en/stable/)
+9. Submit a pull request :-)
 
 [home](https://github.com/RhetTbull/osxphotos/wiki)