Update aws-core.rst (#848)

* Update aws-core.rst

- Change `must` to `SHOULD` in reference to the suffix of `api`, `client`, and `service
- Add guidance to remove the suffix for new SDK versions

* Update docs/source/1.0/spec/aws/aws-core.rst

docs/source/1.0/spec/aws/aws-core.rst

@@ -123,7 +123,7 @@ generating client names in SDKs and for linking between services.
   the first character cannot be a number, and when using spaces, each space must be
   between two alphanumeric characters.
 * The value MUST NOT contain "AWS", "Aws", or "Amazon".
-* The value must not case-insensitively end with "API", "Client", or "Service".
+* The value SHOULD NOT case-insensitively end with "API", "Client", or "Service".
 * The value MUST NOT change change once a service is publicly released. If the value
   does change, the service will be considered a brand new service in the AWS SDKs
   and Tools.
@@ -178,6 +178,10 @@ appending the word "Client" to the final transformed "serviceId". So for the
 
 Other AWS SDKs SHOULD follow a similar pattern when choosing client names.
 
+**Note**:
+For backwards compatibility reasons, some services will include "service" or "API" as a suffix.
+New SDK major versions SHOULD strip ``service`` and ``api`` suffixes from ``sdkId`` when generating
+a client name.
 
 .. _service-cloudformation-name: