Added idea and concept md files

docs/concept.md

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+# Concept
+
+- Homescreen
+  The homescreen of the App should display a list of upcoming tournaments
+  and a button to a tournament you are participating in.
+  If you press on a tournament in the list, the detail view should open
+- Tournament Detail View
+  The tournament detail view displays all the information about a tournament,
+  like
+- The registration period
+- The maximum amount of teams
+- Preview pictures
+- A button for registering your Team if in the registration period
+- A button to view the stats of the tournament if it has been completed or is currently ongoing