TST/DOC #10846 Test and document use of SQLAlchemy expressions in read_sql()
This provides 2 tests using SQLALchemy expressions to read SQL data into a dataframe and accompanying documentation.

It attempts to address #10846 by explaining how this feature is already supported by pandas.

Closes #10846

@stephenpascoe Sorry for the late reply. So this actually already just worked.

Thanks a lot for the tests. And nice docs!

Two questions:
- Can you squash?
- Maybe also add to the `read_sql`/`read_sql_query` docstrings that it can also accept an SQLAlchemy Select statement
 Squashed, docstrings added and rebased.
 Thanks a lot!
