Update README.md

I have updated the readme with three changes:
- Created sections for Installation and Usage to help users
- Added installation instruction
- Added additional example of using LLM. This will be the primary use case and will help users.

README.md

@@ -13,6 +13,14 @@ It presently supports:
 - HTML (special handling of Wikipedia, etc.)
 - Various other text-based formats (csv, json, xml, etc.)
 
+# Installation
+
+You can install `markitdown` using pip:
+
+```python
+pip install markitdown
+```
+# Usage
 The API is simple:
 
 ```python
@@ -23,6 +31,18 @@ result = markitdown.convert("test.xlsx")
 print(result.text_content)
 ```
 
+You can also configure markitdown to use Large Language Models to describe images. To do so you must provide mlm_client and mlm_model parameters to MarkItDown object, according to your specific client.
+
+```python
+from markitdown import MarkItDown
+from openai import OpenAI
+
+client = OpenAI()
+md = MarkItDown(mlm_client=client, mlm_model="gpt-4o")
+result = md.convert("example.jpg")
+print(result.text_content)
+```
+
 ## Contributing
 
 This project welcomes contributions and suggestions.  Most contributions require you to agree to a