src,doc: fix grammar due to missing 'is'

PR-URL: #34897
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

src/README.md

@@ -402,7 +402,7 @@ that state is through the use of `Environment::AddBindingData`, which gives
 binding functions access to an object for storing such state.
 That object is always a [`BaseObject`][].
 
-Its class needs to have a static `binding_data_name` field that based on a
+Its class needs to have a static `binding_data_name` field based on a
 constant string, in order to disambiguate it from other classes of this type,
 and which could e.g. match the binding’s name (in the example above, that would
 be `cares_wrap`).