Add example of full grammar

Author: nvitucci

modules/ROOT/content-nav.adoc

@@ -152,6 +152,7 @@
 *** xref:appendix/gql-conformance/supported-optional.adoc[]
 *** xref:appendix/gql-conformance/analogous-cypher.adoc[]
 *** xref:appendix/gql-conformance/additional-cypher.adoc[]
+** xref:appendix/grammar/index.adoc[]
 ** xref:appendix/tutorials/index.adoc[]
 *** xref:appendix/tutorials/basic-query-tuning.adoc[]
 *** xref:appendix/tutorials/advanced-query-tuning.adoc[]