SyncLanguageServer.create - small documentation note

[Andrej730]

To clarify that relative paths for repositories are not supported.

Currently if it's using relative path, create_server fails with traceback similar to the one below:

Traceback (most recent call last):
  File "third_test.py", line 11, in <module>
    with lsp.start_server():
  File "\Python311\Lib\contextlib.py", line 137, in __enter__
    return next(self.gen)
           ^^^^^^^^^^^^^^
  File "\Python311\Lib\site-packages\multilspy\language_server.py", line 744, in start_server
    asyncio.run_coroutine_threadsafe(ctx.__aenter__(), loop=self.loop).result()
  File "\Python311\Lib\concurrent\futures\_base.py", line 456, in result
    return self.__get_result()
           ^^^^^^^^^^^^^^^^^^^
  File "\Python311\Lib\concurrent\futures\_base.py", line 401, in __get_result
    raise self._exception
  File "\Python311\Lib\contextlib.py", line 210, in __aenter__
    return await anext(self.gen)
           ^^^^^^^^^^^^^^^^^^^^^
  File "\Python311\Lib\site-packages\multilspy\language_servers\jedi_language_server\jedi_server.py", line 101, in start_server
    initialize_params = self._get_initialize_params(self.repository_root_path)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\Python311\Lib\site-packages\multilspy\language_servers\jedi_language_server\jedi_server.py", line 50, in _get_initialize_params
    d["rootUri"] = pathlib.Path(repository_absolute_path).as_uri()
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\Python311\Lib\pathlib.py", line 566, in as_uri
    raise ValueError("relative path can't be expressed as a file URI")
ValueError: relative path can't be expressed as a file URI