docs: embed: add parameters to docstring The docstring of IPython.terminal.embed.embed() does not document its arguments. Add a "Parameters" section, and document each argument appropriately: - for 'header', rephrase the corresponding description from the docstring of InteractiveShellEmbed.__call__, to which this argument is passed (__call__ itself is missing from the generated API documentation since sphinx.ext.autodoc does not document special members by default). - for 'compile_flags', refer to the documentation of InteractiveShellEmbed.mainloop, to which this argument is passed. - for 'kwargs', refer to the constructor of InteractiveShellEmbed, and fold in the sentence mentioning the 'config' argument.