docs: update ollama usage readme (#301)

Signed-off-by: Albert Simon <albert.simon.sge@mango.com>
Co-authored-by: Albert Simon <albert.simon.sge@mango.com>

Author: willyw0nka

README.md

@@ -68,7 +68,7 @@ You can also run it with local model through ollama:
 
 ```sh
 git add <files...>
-AI_PROVIDER='ollama' opencommit
+OCO_AI_PROVIDER='ollama' opencommit
 ```
 
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