Add information on how to add new provider

CONTRIBUTING.md

@@ -43,6 +43,21 @@ Then just run the `./autogen.sh` to generate the added or updated node classes.
 [black]: https://pypi.org/project/black
 [inkscape]: https://inkscape.org/ko/release
 
+### Add new provider
+
+To add a new provider to Diagrams, please follow the steps below in addition to the image intructions above:
+- in `autogen.sh` add in the `providers` variable the new provider code
+- in `config.py`:
+  - in the `providers` variable, add the new provider code
+  - in the `FILE_PREFIXES` variable, add a new entry with your new provider code. And eventually a file prefix
+  - Optionnaly, update the `UPPER_WORDS` variable to a new entry with your new provider code.
+  - in the `ALIASES` variable, add a new entry with your new provider code. See below on how to add new aliases.
+- in `scripts/resource.py`:
+  - add a function `cleaner_XXX` (replace XXX by your provider name). For the implementation look at the existing functions
+  - in the `cleaners` variable, add an entry with your new provider code and the function defined above
+- in `sidebars.json`, update the `Nodes` array to add the reference of the new provider
+- in the `diagrams` folder, add a new file `__init__.py` for the new provider. For the content look at the existing providers
+
 ### Update Aliases
 
 Some node classes have alias. For example, `aws.compute.ECS` class is an alias