Update docs to point to Read the Docs
MODIFY
docs/README.md
docs/README.md
## Documentation
-The SES documentation is hosted by Read the Docs, and is built using
+The [SES documentation](https://ses-secure-ecmascript.readthedocs.io/en/latest/) is hosted by Read the Docs, and is built using
[Sphinx](https://docs.readthedocs.io/en/stable/intro/getting-started-with-sphinx.html).

Update docs to point to Read the Docs (#117)