convention is to start sentence with upper case

Author: tshepang

src/conventions.md

@@ -50,7 +50,8 @@ When modifying Python code, use this command to format it:
 ./x test tidy --extra-checks py:fmt --bless
 ```
 
-and the following command to run lints:
+And, the following command to run lints:
+
 ```console
 ./x test tidy --extra-checks py:lint
 ```