Main: Added documentation welcome page

src/main.cpp

@@ -12,6 +12,32 @@
  *    2) get password from stdin
  *    3) process the user's request (i.e. print a list of
  *       available messages or download a specific message)
+ *
+ * @mainpage pop3client documentation
+ *  Welcome to pop3client documentation. Hopefully you'll find here
+ *  exactly what you need!
+ *
+ *  pop3client is a simple program that is able to connect to
+ *  remote POP3 server and list/download messages from there.
+ *
+ *  It was developed as a part of Seznam.cz job try-out.
+ *
+ * @section license License
+@verbatim
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+@endverbatim
+ *
  */
 
 #include <iostream>