Add example description

Since sats are brought up for the first time in this example, it might be useful to explain what sats and millisats are.

value/value.md

@@ -107,6 +107,11 @@ exists at the `<item>` level, it is intended to override the channel level tag f
 
 #### Example:
 
+The following example uses the `keysend` method of the `lightning` Network and
+sets the suggested value to 5 sats. A sat, short for satoshi, is a one hundred
+millionth of a single bitcoin (0.00000001 BTC). The smallest unit on the
+Lightning Network is a millisat, which is a thousandth of a sat.
+
 ```xml
 <podcast:value
     type="lightning"