Section 6.6 of the Apache Beam Python programming guide lacks examples

In the section "Using Schema Transforms" of the Python programming guide, which can be found [here](https://beam.apache.org/documentation/programming-guide/#using-schemas), there are missing examples. e.g.
##### *Nested fields*

Individual nested fields can be specified using the dot operator. For example, to select just the postal code from the shipping address one would write
##### *Wildcards*

The * operator can be specified at any nesting level to represent all fields at that level. For example, to select all shipping-address fields one would write

These paragraphs are eerily similar to the ones that can be found on the Java programming guide, but they have their corresponding examples.

Imported from Jira [BEAM-12825](https://issues.apache.org/jira/browse/BEAM-12825). Original Jira may contain additional context.
Reported by: edusan.