add note to grammar about changes

src/parser/sparqlParser/generated/SparqlAutomatic.g4

@@ -195,7 +195,9 @@ quads: triplesTemplate? ( quadsNotTriples '.'? triplesTemplate? )* ;
 
 quadsNotTriples: GRAPH varOrIri '{' triplesTemplate? '}' ;
 
-// triplesTemplate: triplesSameSubject ( '.' triplesTemplate? )?;
+// We have replaced the original recursive definition with an equivalent
+// non-recursive definition for performance reasons.
+// Original definition: `triplesTemplate: triplesSameSubject ( '.' triplesTemplate? )?;`
 triplesTemplate: triplesSameSubject ( '.' triplesSameSubject )* '.'? ;