Add accepted format type to load_seq function

[cthwe]

Put format type in the help section so people know what's available

[KatherineCaley]

add basic usage

[GavinHuttley]

The supported file suffixes are the keys to cogent3.parse.sequence.PARSERS. Including these in the docstring is either done by:

1. manually: which is bad because that can get out-of-date
2. automagically: requires a decorator that operates like "cogent3.util.misc.extend_docstring_from"

Potentially modify the latter decorator so it can be used like

import textwrap

_known_parsers = textwrap.wrap(", ".join(PARSERS), width=80, break_long_words=False, break_on_hyphens=False)

@extend_docstring_from(replace="KNOWN", with=_known_parsers)
def some_func():
    """my summary line
    
    Notes
    ------
    support suffixes are: KNOWN
    """

which results in

>>> help(some_func)
Help on function some_func in module __main__:

some_func()
    my summary line
    
    Notes
    ------
    support suffixes are: fa, fasta, ...