Add docs in README.md

README.md

@@ -1 +1,25 @@
-# contracts-compatibility
+# Dolittle Contracts Compatibility tool
+
+The `contracts-compatibility` checks what versions of the Dolittle [Runtime](https://github.com/dolittle/Runtime) and
+SDKs that are compatible with each other. And can generate a Markdown table or a JSON structure. Currently, the tool
+checks the [DotNet SDK](https://github.com/dolittle/DotNET.SDK) and the
+[JavaScript SDK](https://github.com/dolittle/JavaScript.SDK). It was built to generate the compatibility table on
+[dolittle.io](https://dolittle.io/docs/reference/runtime/compatibility/), and for other internal uses.
+
+Usage:
+```shell
+contracts-compatibility -h
+Contracts Compatibility a tool to resolve compatible versions of the Dolittle Runtime and SDKs
+Usage:
+  -h    Print help information
+  -o string
+        Output format [markdown,json] (default "markdown")
+```
+
+Running the tool fetches all currently released versions from the public repositories, and resolves the compatible
+versions.
+
+> **Warning**: for the Runtime, the tool fetches the Docker manifests from Docker Hub without authentication. Since
+> there are quite a few released versions, this quickly eats into your IPs rate limits. So be careful about running it
+> a lot of times. Read more on the
+> [Docker Hub rate limit documentation](https://docs.docker.com/docker-hub/download-rate-limit/#definition-of-limits).