editable: grammar fix

Author: sbidoul

pep-0657.rst

@@ -115,7 +115,7 @@ with the exception that they can add dependencies necessary for their editable
 mechanism to function at runtime (such as `editables`_).
 
 The filename for the “editable” wheel need not use the same tags as
-``build_wheel`` but must be tagged as compatible with the system.
+``build_wheel`` but it must be tagged as compatible with the system.
 
 An “editable” wheel uses the wheel format not for distribution but as ephemeral
 communication between the build system and the front end. This avoids having