DOC: fixed documentation about spherical caps

[alessio26gas]

Pull request type

• Code changes (bugfix, features)
• Code maintenance (refactoring, formatting, tests)
• ReadMe, Docs and GitHub updates
• Other

Current behavior

The existing documentation for the spherical_caps parameter currently states:

The spherical_caps parameter is optional and defaults to False. If set
to True, the tank will be defined as a cylinder with flat caps.
If True, the tank will have spherical caps.

New behavior

This should be updated to:

The spherical_caps parameter is optional and defaults to False. If set
to True, the tank will have spherical caps at the top and bottom with the
same radius as the cylindrical part. If set to False, the tank will
be defined as a cylinder with flat caps.

Breaking change

• Yes
• No

[Gui-FernandesBR]

Nice catch!