examples: add Interesting snippet tags to examples and link in Readme.md

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

examples/analogin_a0.c

@@ -31,6 +31,7 @@ int main ()
     maa_aio_context adc_a0;
     uint16_t adc_value = 0;
 
+//! [Interesting]
     adc_a0 = maa_aio_init(0);
     if (adc_a0 == NULL) {
         return 1;
@@ -42,6 +43,7 @@ int main ()
     }
 
     maa_aio_close(adc_a0);
+//! [Interesting]
 
     return MAA_SUCCESS;
 }