Added brief explantation of the sensors creation (home-assistant#3675)

quaec · fabaff · commit 2005b310cc57 · 2017-10-21T09:56:29.000+02:00
diff --git a/source/_components/binary_sensor.http.markdown b/source/_components/binary_sensor.http.markdown
@@ -12,6 +12,10 @@ ha_category: Binary Sensor
 ha_release: pre 0.7
 ---
 
+The HTTP binary sensor is dynamically created with the first request that is made to its URL. You don't have to define it in the configuration first.
+
+The sensor will then exist as long as Home Assistant is running. After a restart of Home Assistant the sensor will be gone until it is triggered again.
+
 The URL for a binary sensor looks like the example below:
 
 ```bash
