Add info on userver framework

Author: apolukhin

README.md

@@ -944,6 +944,7 @@ A curated list of awesome C++ (or C) frameworks, libraries, resources, and shiny
 * [Pistache](http://pistache.io/) - Pistache is a C++ REST framework written in pure C++11 with no external dependency. [Apache2]
 * [QDjango](https://github.com/jlaine/qdjango/) - A web framework written in C++ and built on top of the Qt library. Where possible it tries to follow django's API, hence its name. [LGPL]
 * [TreeFrog Framework](https://github.com/treefrogframework/treefrog-framework) - High-speed and full-stack web application framework based on C++ and Qt, which supports HTTP and WebSocket protocol (with O/R mapping). [BSD] [website](http://www.treefrogframework.org/)
+* [userver](https://github.com/userver-framework/userver) - Asynchronous C++17 framework with a rich set of abstractions and database drivers for fast and comfortable creation of efficient microservices, services and utilities. [Apache-2.0] [website](https://userver.tech/)
 * [Wt](http://www.webtoolkit.eu/wt) - A C++ library for developing web applications. [GPL/Commercial]
 
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