Add example to demo ADC channel usage

diff --git a/examples/adc.py b/examples/adc.py
new file mode 100755 (executable)
index 0000000..c4cf45c
--- /dev/null
+++ b/examples/adc.py
@@ -0,0 +1,21 @@
+#!/usr/bin/env python
+
+import time
+from enviroplus import gas
+
+print("""adc.py - Print readings from the MICS6814 Gas sensor.
+
+Press Ctrl+C to exit!
+
+""")
+
+gas.enable_adc()
+gas.set_adc_gain(4.096)
+
+try:
+    while True:
+        readings = gas.read_all()
+        print(readings)
+        time.sleep(1.0)
+except KeyboardInterrupt:
+    pass