Apply suggestions from code review

Co-authored-by: Armin Ruech <[email protected]>

CONTRIBUTING.md

@@ -210,12 +210,13 @@ exists in some form in ECS, consider the following guidelines:
     data, user issue reports, feature requests, examples of prior work on a
     different standard or comparable evidence about the alternatives.
   - When no suitable alternatives are provided, altering an ECS name solely
-    for the purpose of complying with [Name Pluralization guidelines](https://opentelemetry.io/docs/specs/otel/common/attribute-naming/#name-pluralization-guidelines)
+    for the purpose of complying with [Name Pluralization guidelines](docs/general/attribute-naming.md#name-pluralization-guidelines)
     MAY BE avoided.
 - Do not use an existing ECS name as a namespace. If the name must differ, use a
   different namespace name to avoid clashes or avoid using the namespace
-  entirely.
+  entirely. See the [ECS field reference] for existing namespaces.
 
 [nvm]: https://github.com/nvm-sh/nvm/blob/master/README.md#installing-and-updating
 [stability guarantees]: https://github.com/open-telemetry/opentelemetry-specification/blob/v1.26.0/specification/versioning-and-stability.md#semantic-conventions-stability
 [otep222]: https://github.com/open-telemetry/oteps/pull/222
+[ECS field reference]: https://www.elastic.co/guide/en/ecs/current/ecs-field-reference.html