DOC: Update docstring of DataFrame/Series .equals() to explain the behavior with indices
Some work and some discussion happened at #19213.

`df1.equals(df2)` returns a single boolean value on whether the two dataframes contain the same values and indices. This includes types for the data, but not for the indices.

The docstring should be improved to follow all our standards, including:
- A `See Also` section that at least links to `.eq()`
- `Parameters`
- `Examples`
- `Notes` with the mentioned behavior about indices