main: Fix 'N' clear new notification flag documentation

The documentation for the 'N' key wrongly stated it clears all
notifications. But in the code we see that just the new notification
flag is reset.

Author: NeroBurner

README.md

@@ -96,7 +96,7 @@ Using the keyboard the following events can be triggered:
 - `m` ... let motor run for 100 ms
 - `M` ... let motor run for 255 ms
 - `n` ... send notification
-- `N` ... clear all notifications
+- `N` ... clear new notification flag
 - `b` ... connect Bluetooth
 - `B` ... disconnect Bluetooth
 - `v` ... increase battery voltage and percentage

main.cpp

@@ -773,7 +773,7 @@ class Framework {
 private:
     bool key_handled_r = false; // r ... enable ringing, R ... disable ringing
     bool key_handled_m = false; // m ... let motor run, M ... stop motor
-    bool key_handled_n = false; // n ... send notification, N ... clear all notifications
+    bool key_handled_n = false; // n ... send notification, N ... clear new notification flag
     bool key_handled_b = false; // b ... connect Bluetooth, B ... disconnect Bluetooth
     bool key_handled_v = false; // battery Voltage and percentage, v ... increase, V ... decrease
     bool key_handled_c = false; // c ... charging, C ... not charging