update documentation

app.py

@@ -16,6 +16,7 @@ It uses the model developped to detect if a tweet has hate speech or not
 This is a Machine Learning endpoint that predict if a text is a hate speech or not with a certain degree of certainity. Here is the endpoint:
 
 * `/predict` that accepts string value
+* `/preprocess` that accepts string value
 
 
 Check out documentation below 👇 for more information on each endpoint.