TO Betty Kadoorie, the engaging Cuban wife of industrialist Michael Kadoorie, we attribute the Thought Of The Week. Meeting up at a dinner the other night with Betty - who enlivens any occasion with her fun-filled presence - she referred to the Keeping Posted item about the Bayanihan Trust, which is trying to raise money to provide civic centres for overseas domestic workers. Noted Betty: ''There are supposed to be 100,000 maids working in Hong Kong. So if everyone employing a maid donated just $100 for every maid who worked for them the trust would have $10 million.'' Incidentally, at the colourful fiesta which helped launch the Bayanihan Trust was concert promoter Anders Nelsson who offered a suggestion of his own. He wondered: ''How about the new Hong Kong Stadium as a gathering place for the maids on Sunday?''