chore: add stability policy to SDK docs (awslabs#614)

Author: jbelkins

README.md

@@ -2,7 +2,7 @@
 
 The **AWS SDK for Swift** is a pure Swift SDK for AWS services.
 
-**WARNING: Releases prior to 1.0.0 may contain bugs and no guarantee is made about API stability. They are not intended for use in production!**
+**The AWS SDK for Swift is currently in developer preview and is intended strictly for feedback purposes only. Do not use this SDK for production workloads. Refer to the SDK [stability](docs/stability.md) guidelines for more detail.**
 
 ## License
 

docs/stability.md

@@ -0,0 +1,25 @@
+# Stability of the AWS SDK for Swift
+
+For information about maintenance and support of SDK major versions and their underlying dependencies, see the
+following in the AWS SDKs and Tools Shared Configuration and Credentials Reference Guide:
+
+* [AWS SDKs and Tools Maintenance Policy](https://docs.aws.amazon.com/credref/latest/refdocs/maint-policy.html)
+* [AWS SDKs and Tools Version Support Matrix](https://docs.aws.amazon.com/credref/latest/refdocs/version-support-matrix.html)
+
+## Qualifiers
+
+Qualifiers for published artifacts
+
+**`-alpha`** indicates:
+
+* The SDK is not meant for production workloads. It is released solely for the purpose of getting feedback.
+* The SDK is not yet feature complete. It may contain bugs and performance issues.
+* Expect migration issues as APIs/types change.
+
+**`-beta`** indicates:
+
+* The SDK is not meant for production workloads. 
+* The SDK is feature complete. It may still contain bugs and performance issues.
+* The APIs/types are mostly stabilized. It is still possible that future releases may cause migration issues.
+
+NOTE: This corresponds to the "Developer Preview" phase of the maintenance policy linked above.