docs: add notes on attribute key descriptor (#155)

Co-authored-by: Valentin Marchaud <contact@vmarchaud.fr>

Author: legendecas

src/common/Attributes.ts

@@ -16,6 +16,8 @@
 
 /**
  * Attributes is a map from string to attribute values.
+ *
+ * Note: only the own enumerable keys are counted as valid attribute keys.
  */
 export interface Attributes {
     [attributeKey: string]: AttributeValue | undefined;

src/trace/attributes.ts

@@ -17,11 +17,11 @@
 import { Attributes, AttributeValue } from '../common/Attributes';
 
 /**
- * @deprecated please use Attributes
+ * @deprecated please use {@link Attributes}
  */
 export type SpanAttributes = Attributes;
 
 /**
- * @deprecated please use AttributeValue
+ * @deprecated please use {@link AttributeValue}
  */
 export type SpanAttributeValue = AttributeValue;