feat: declare copyright ownership

src/grammar/trinosql/TrinoSql.g4

@@ -1,3 +1,22 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * This file is an adaptation of trino's trino/core/trino-parser/src/main/antlr4/io/trino/sql/parser/SqlBase.g4 grammar.
+ * Reference: https://github.com/trinodb/trino/blob/385/core/trino-parser/src/main/antlr4/io/trino/sql/parser/SqlBase.g4
+ */
+
 grammar TrinoSql;
 
 tokens {