Add project status in the readme

Closes #894

README.md

@@ -271,3 +271,7 @@ int main() {
   Http::listenAndServe<HelloHandler>(Pistache::Address("*:9080"));
 }
 ```
+
+## Project status
+
+Pistache hasn't yet hit the 1.0 release. This means that the project is _unstable_ but not _unusable_. In fact, most of the code is production ready; you can use Pistache to develop a RESTful API without issues, but the HTTP client has a few issues in it that make it buggy.