opentelemetry-sdk: clarify Resource.create usage

After #3181 ResourceDetector instances cannot call Resource.create
otherwise when using auto-instrumentation you'll go into an infinite loop
trying to load resource detectors.

opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py

@@ -23,7 +23,8 @@
     these attributes can be included in the Resource.*
 
 Resource objects are created with `Resource.create`, which accepts attributes
-(key-values). Resources should NOT be created via constructor, and working with
+(key-values). Resources should NOT be created via constructor yet ResourceDetector
+instance can't use `Resource.create` to avoid infinite loops. Working with
 `Resource` objects should only be done via the Resource API methods. Resource
 attributes can also be passed at process invocation in the
 :envvar:`OTEL_RESOURCE_ATTRIBUTES` environment variable. You should register
@@ -175,6 +176,8 @@ def create(
     ) -> "Resource":
         """Creates a new `Resource` from attributes.
 
+        This is supposed to be called by the SDK and not by ResourceDetector instances.
+
         Args:
             attributes: Optional zero or more key-value pairs.
             schema_url: Optional URL pointing to the schema