By Hyunjoo Jin and Akash Sriram (Reuters) -Billionaire entrepreneur Elon Musk said on Friday he planned to “significantly” increase childcare benefits at his companies, including Tesla Inc, and that the details likely would be announced next month. His comments came a day after Musk tweeted that he will do his best to help what he called “the underpopulation crisis,” following a media report that said he had secret twins with a top executive at his brain-chip start-up Neuralink. “Kids are worth it if at all possible. I’m planning to increase childcare benefits at my companies significantly,” M…