PIP-0021: fix github flavor markdown inconsistency

PIP/PIP-0021.md

@@ -47,16 +47,23 @@ The following rules apply unless the context requires otherwise:
 > A clause structured as:
 > 
 >    _"50. Parent Clause Title
+>
 >    The XXX agree
+>
 >        50.1 to do UUU. 
+>
 >        50.2 to do VVV.  
+>
 >    The YYY agree
+>
 >        50.3 to do WWW."_
 > 
 >shall be interpreted as:
 > 
 >    _"50.1 The XXX agree to do UUU.
+>
 >    50.2 The XXX agree to do VVV.
+>
 >    50.3 The YYY agree to do WWW."_
 
 ## TERMS AND CONDITIONS