Add note that namespace and pacakges are suggestions not hard rules (#23)

Author: JBD

NamespaceAndPackage.md

@@ -2,17 +2,21 @@
 
 ## Introduction
 This document describes the key package names (namespaces, etc.).
+This is only a guideline, language implementations should
+consider the best option to be idiomatic.
 
 ## Structure
 The top level package name MUST be **opencensus** (for URL model MUST use **io.opencensus**).
 
-The second level package names MUST be:
+The second level package names SHOULD be:
 * **stats**: for all measurement related functionality
 * **tags**: for all tagging related functionality
 * **context**: for all context related functionality
 * **trace**: for all trace functionality
-* **common**: for all public API components that are shared across multiple of the above. These are
+* **common**: for all public API components that are shared across multiple of the above^*^. These are
 typically utility classes such as timestamps, etc.
 * **internal**: If required, "internal" subdirectories/names of each of the above SHOULD be used
 for all internal API components. e.g. common internal can have utility classes such as providers,
-string manipulation, etc.
+string manipulation, etc.
+
+(^*^): For Go, consider using the top-level package instead.