Fix: price auto adjust confusion

[ValueRaider]

Fix user confusion from not knowing auto_adjust by telling them to set it. Might resolve #1982 and similar older issues.

[JanMkl]

This would be one way to clear the confusion like on issue #2332, #2302 and #2283.

The change seems quite polite and won't make the yfinance too noisy. If more attention is wanted then one could add short sleep after the print like:

        if not _warned_auto_adjust:
            warnings.warn("You have not set argument 'auto_adjust'. This defaults to False, but you should be setting it (Yahoo sets to True).", UserWarning)
            _warned_auto_adjust = True
            time.sleep(3)  # Pause execution for 3 seconds

[ValueRaider]

yf already prints something like that