doc: update readme.md (#45)

* doc: update readme.md

Signed-off-by: Yi Zha <yizha1@microsoft.com>

README.md

@@ -1,13 +1,15 @@
 # TUF
 
+This repository is **not** in active maintenance. Please see the Notary Project [README](https://github.com/notaryproject/.github/blob/main/README.md) file to learn about overall Notary Project.
+
 TUF is a project to implement the full TUF specification in a registry native way. This may
 require upstream TUF spec changes or extensions, as there are some differences between the
 registry model and common usage to other TUF use cases. This project will use existing
 registry extensions where available but may need its own document types in addition.
 
-The initial version of Notary ran as an additional service on a registry, so was not
+The notary TUF-based implementation ran as an additional service on a registry, so was not
 available everywhere and did not create native registry artifacts. In turn this meant
-that moving signatures between registries was not supported. Notary also made some
+that moving signatures between registries was not supported. The notary TUF-based implementation also made some
 changes to the TUF security model, like defaulting to TOFU, which in retrospect were
 not a good model in a world of ephemeral cloud native hosts. It did not get widespread
 adoption due to these reasons and others. This project aims to build a version suitable