Ellen Pao resigned as acting chief executive of Reddit Friday in the latest sign of turmoil at the site, recently roiled by the firing of a popular employee and ongoing tensions over the limits of free speech on its social-news platform. Reddit co-founder Steve Huffman, also a co-founder of travel site Hipmunk, will become chief executive. Alexis Ohanian, another co-founder who has been working as executive chairman of reddit, will work “alongside” Huffman, said Reddit board head Sam Altman in a statement on Friday.