Documentation Request for Using RSCU param with `python_codon_tables`

Just like it sounds. It'd be great to see how to use the RSCU param in the docs. In particular how to integrate it with the value from `python_codon_tables.get_codons_table()`.

Most of the examples are using a reference genome and I get key errors when I try:

```
RSCU = python_codon_tables.get_codons_table("h_sapiens")
initial_grade = CAI.CAI(initial_seq, RSCUs=RSCU)
```

Start by reading the existing examples that use a reference genome and inspect the `python_codon_tables.get_codons_table()` and `CAI.CAI(..., RSCUs=...)` entry points. Update the documentation with a working integration example and verify that it addresses the reported key errors.

Written by the indexing model from the issue text.