User doc intro

Rewritten-docs.md

@@ -1722,9 +1722,16 @@ applications.
 
 # User documentation
 
-@todo: Describe different scenarios of the usage of the Web App
+Users interact with the ReCodEx through the web application. For the best user experience we strongly recommend to use modern web browsers with enabled `CSS` and mostly `Javascript`. Another features which are necessary to proper work with application are `Cookies` and browser `Local storage`.
 
-@todo: Describe the requirements of running the web application (modern web browser, enabled CSS, JavaScript, Cookies & Local storage)
+Supported and tested browsers are: Firefox 50+, Chrome 55+, Opera 42+ and Edge 13+. Mobile devices are not officially supported and it is possible that application will not work properly there.
+
+Usage of the web application is divided into the sections concerning the particular user roles. Under these sections all possible use cases can be found. Used roles are:
+
+- Student
+- Group supervisor
+- Group administrator
+- Superadministrator
 
 ## Terminology
 
@@ -1755,8 +1762,6 @@ They can be shared by the teachers using an exercise database in ReCodEx.
 
 @todo: actions which are available for all users
 
-@todo: how to solve problems with ReCodEx, first supervisors, then administrators, etc...
-
 ### First steps in ReCodEx
 
 You can create an account if you click on the “*Create account*” menu