Merge pull request bitcoin#1417 from achow101/380-clarify-optional-checksum

380: Clarify optionality of descriptor checksum

Author: kallewoof

bip-0380.mediawiki

@@ -49,6 +49,7 @@ Lastly, the use of common terminology and existing standards allow for Output Sc
 Descriptors consist of several types of expressions.
 The top level expression is a <tt>SCRIPT</tt>.
 This expression may be followed by <tt>#CHECKSUM</tt>, where <tt>CHECKSUM</tt> is an 8 character alphanumeric descriptor checksum.
+Although the checksum is optional for parsing, applications may choose to reject descriptors that do not contain a checksum.
 
 ===Script Expressions===