doc: fix md issue in src/README.md

PR-URL: #33224
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

src/README.md

@@ -395,7 +395,7 @@ void Initialize(Local<Object> target,
 NODE_MODULE_CONTEXT_AWARE_INTERNAL(cares_wrap, Initialize)
 ```
 
-<a id="per-binding-state">
+<a id="per-binding-state"></a>
 #### Per-binding state
 
 Some internal bindings, such as the HTTP parser, maintain internal state that