docs: fix grammar in first steps tutorial

Fixes a minor grammatical issue in the First Steps documentation.

docs/en/docs/tutorial/first-steps.md

@@ -54,7 +54,8 @@ In the output, there's a line with something like:
 INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
 ```
 
-That line shows the URL where your app is being served, in your local machine.
+That line shows the URL where your app is being served on your local machine.
+
 
 ### Check it { #check-it }