Clarification for MCP23017 (#1854)

components/mcp230xx.rst

@@ -146,6 +146,9 @@ pins for your projects. Within ESPHome they emulate a real internal GPIO pin
 and can therefore be used with many of ESPHome's components such as the GPIO
 binary sensor or GPIO switch.
 
+GPIO pins in the datasheet are labelled A0 to A7 and B0 to B7, these are mapped
+consecutively in this component to numbers from 0 to 15.
+
 .. code-block:: yaml
 
     # Example configuration entry
@@ -156,10 +159,10 @@ binary sensor or GPIO switch.
     # Individual outputs
     switch:
       - platform: gpio
-        name: "MCP23017 Pin #0"
+        name: "MCP23017 Pin A0"
         pin:
           mcp23xxx: mcp23017_hub
-          # Use pin number 0
+          # Use pin A0
           number: 0
           mode:
             output: true
@@ -168,11 +171,11 @@ binary sensor or GPIO switch.
     # Individual inputs
     binary_sensor:
       - platform: gpio
-        name: "MCP23017 Pin #1"
+        name: "MCP23017 Pin B7"
         pin:
           mcp23xxx: mcp23017_hub
-          # Use pin number 1
-          number: 1
+          # Use pin B7
+          number: 15
           # One of INPUT or INPUT_PULLUP
           mode:
             input: true