XML tags moved to Appendix D of Ecma-334

The 5th Edition / December 2017  of https://www.ecma-international.org/publications/files/ECMA-ST/ECMA-334.pdf
has the XML commands in Appendix D

Fix issue Typo in xmlcmds.doc XML tags moved to Appendix D of Ecma-334 doxygen#7855
  doxygen#7855

Author: d-c-d

doc/xmlcmds.doc

@@ -17,7 +17,7 @@
 /*! \page xmlcmds XML Commands
 
 Doxygen supports most of the XML commands that are typically used in C# 
-code comments. The XML tags are defined in Appendix E of the
+code comments. The XML tags are defined in Appendix D of the
 <a href="http://www.ecma-international.org/publications/standards/Ecma-334.htm">ECMA-334</a> 
 standard, which defines the C# language. Unfortunately, the specification is
 not very precise and a number of the examples given are of poor quality.