Update README.md

Added a more detailed usage explaination

Author: SapuSeven

README.md

@@ -3,3 +3,15 @@
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 NotiCap executes SSH commands when receiving a notification from a specific application.
+
+## Usage
+
+After installation, you first have to grant NotiCap notification access.
+
+To do this, go to _Filter Rules->Setup_, search for NotiCap in the displayed list and enable notification access.
+
+The next step is to setup your first identity at _SSH Identities->Add SSH Identity_.
+
+Finally, go back to _Filter Rules_ and select _Add Filter Rule_.
+
+_Note: The Filter Rule screen only provides very basic options at the moment. If you miss a specific function, feel free to add it and submit a Pull Request or open a new issue._