docs: add list with alternative implementations (#169)

Add comparison to Notary

explain difference between notary and go-tuf

Signed-off-by: Marina Moore <mnm678@users.noreply.github.com>
Signed-off-by: Marina Moore <mnm678@gmail.com>
Co-authored-by: Trishank Karthik Kuppusamy <trishank.kuppusamy@datadoghq.com>

README.md

@@ -653,3 +653,10 @@ install tuf`). To update the data for these tests requires Docker and make (see
 test data [README.md](client/python_interop/testdata/README.md) for details).
 
 Please see [CONTRIBUTING.md](docs/CONTRIBUTING.md) for contribution guidelines before making your first contribution!
+
+## Comparison to other implementations
+
+There are TUF implementations in a variety of programming languages. Some other Go implementations of TUF include:
+
+* [Notary](https://github.com/notaryproject/notary): A version of TUF designed specifically for publishing and managing trusted collections of content. It was used by Docker Content Trust, and has since been superseded by the [Notation](https://github.com/notaryproject/notation) project. In contrast, go-tuf is a direct implementation of TUF and has been updated to conform to 1.0.0 of the TUF specification.
+