Fix CreateAttachment documentation to describe as struct

[limonfort]

This pull request addresses issue #2889 by correcting the documentation for the CreateAttachment struct. The previous documentation incorrectly described CreateAttachment as an enum and stated that it allows a user to pass a Path or a File type to send_files, which was misleading.

Changes made in this pull request:

• Corrected the documentation for CreateAttachment to accurately reflect that it is a struct.
• Updated the description to explain that CreateAttachment allows a user to create an attachment from raw data, a file path, a file handle, or a URL.

This fix ensures that developers have accurate and useful information when using the CreateAttachment struct in their applications.

Fixes #2889

[jamesbt365]

please run cargo +nightly fmt --all.

[limonfort]

fixed now i think