Position Lara at the right side of the doorway facing down the slope. Turn her about 30 degrees to the left, as shown in the screenshot above.
Take a standing jump forward onto the first low block beyond the higher angled blocks on the left side of the long slide (i.e., the first one that slopes down toward the slide, shown above). Keep holding the Jump key, and she'll backflip off that block and then take a series of forward jumps along the right side of the slope. On the third jump, she'll spring back across the slope to the left side.
At that point, release the Jump key to slide down the last slope and land in a doorway.