Update How_to_contribute.md

How_to_contribute.md

@@ -104,9 +104,9 @@ Additionally, if any conversion is required on the input or output cost/token, y
 
 ```python
 def compute_cost_per_token(self, input_cost_per_token, output_cost_per_token, labor):
-#Additional computation on your cost_per_token values
-#You often need to convert some values here
-return input_cost_per_token, output_cost_per_token, labor
+  #Additional computation on your cost_per_token values
+  #You often need to convert some values here
+  return input_cost_per_token, output_cost_per_token, labor
 ```
 
 Once your model class is ready, you’ll have to **add it to the `models.py` file** in our TCO Calculator’s [Hugging Face repository](https://huggingface.co/spaces/mithril-security/TCO_calculator/tree/main).