DOC: document different syntax depending on muparserver version

Applications/Utils/otbBandMath.cxx

@@ -57,7 +57,10 @@ private:
 
     SetDocName("Band Math");
     SetDocLongDescription("This application performs a mathematical operation on monoband images."
-      " Mathematical formula interpretation is done via MuParser libraries http://muparser.sourceforge.net/");
+      " Mathematical formula interpretation is done via MuParser libraries http://muparser.sourceforge.net/." 
+      "For MuParser version prior to v2 use 'and' and 'or' logical operators, and ternary operator 'if( ; ; )'." 
+      "For MuParser version superior to 2.0 uses '&&' and '||' logical operators, and C++ like ternary if-then-else operator.");
+
     SetDocLimitations("None");
     SetDocAuthors("OTB-Team");
     SetDocSeeAlso(" ");