astype documentation lacks a section about the copy parameter

[prcastro]

The astype method of both DataFrame and Series don't include an explanation about the copy parameter in 'parameters' session.

[gfyoung]

@prcastro : Thanks for reporting this! We just added a section to the issues template about checking the docs on master at https://pandas-docs.github.io/pandas-docs-travis.

If you look at the corresponding links for DataFrame and Series, you will see that we have addressed your issue already 👍

See #17203 for the changes. Closing since this issue has already been resolved. Will re-open if you have any other concerns related to the copy parameter.