Add entry for new example

Author: pramsey

examples/README.md

@@ -4,6 +4,7 @@
 * `capi_read_ts` uses the "re-entrant" C API (threadsafe) to read two WKT geometries, calculate the intersection and print the result
 * `capi_prepared` uses the standard C API to read one WKT geometry, and fill it with a point grid, applying a high performance "prepared" geometry to speed up intersection testing
 * `capi_strtree` uses the standard C API to build a random collection of points, and then search that collection quickly to find the nearest to a query point
+* `capi_indexed_predicate` uses the standard C API API to build an STRtree index on a custom class, and then query that index with a prepared geometry, returning a list of matching items
 * `cpp_read` uses the C++ API to read two WKT geometries, calculate the intersection and print the result
 * `cpp_strtree` uses the C++ API to build an STRtree index on a custom class, and then query that index