Add advanced_parquet_index.rs example of indexing into parquet files

Author: alamb

datafusion-examples/README.md

@@ -45,6 +45,7 @@ cargo run --example csv_sql
 - [`advanced_udaf.rs`](examples/advanced_udaf.rs): Define and invoke a more complicated User Defined Aggregate Function (UDAF)
 - [`advanced_udf.rs`](examples/advanced_udf.rs): Define and invoke a more complicated User Defined Scalar Function (UDF)
 - [`advanced_udwf.rs`](examples/advanced_udwf.rs): Define and invoke a more complicated User Defined Window Function (UDWF)
+- ['advanced_parquet_index.rs'](examples/advanced_parquet_index.rs): Creates a detailed secondary index that covers the contents of several parquet files
 - [`avro_sql.rs`](examples/avro_sql.rs): Build and run a query plan from a SQL statement against a local AVRO file
 - [`catalog.rs`](examples/catalog.rs): Register the table into a custom catalog
 - [`csv_sql.rs`](examples/csv_sql.rs): Build and run a query plan from a SQL statement against a local CSV file