Add supported apis to readme (#15)

Author: TheoKanning

README.md

@@ -8,6 +8,17 @@ Includes the following artifacts:
 
 as well as an example project using the client.
 
+## Supported APIs
+- [Engines](https://beta.openai.com/docs/api-reference/engines)
+- [Completions](https://beta.openai.com/docs/api-reference/completions)
+- [Edits](https://beta.openai.com/docs/api-reference/edits)
+- [Searches](https://beta.openai.com/docs/api-reference/searches)
+- [Classifications](https://beta.openai.com/docs/api-reference/classifications)
+- [Answers](https://beta.openai.com/docs/api-reference/answers)
+- [Files](https://beta.openai.com/docs/api-reference/files)
+- [Fine-tunes](https://beta.openai.com/docs/api-reference/fine-tunes)
+- [Embeddings](https://beta.openai.com/docs/api-reference/embeddings)
+
 ## Usage
 
 ### Importing into a gradle project