Update README.md on OpenCL usage

Author: burjui

README.md

@@ -1,4 +1,4 @@
 <blockquote><sub>"Collision! My misssion!"<br/>Faith No More</sub></blockquote>
 
 This is an experiment in particle system simulation.
-Currently uses 4th order Leapfrog integrator with Yoshida coefficients and preserves momentum on collisions if `restitution_coefficient = 1` (see config.toml). Runs on CPU, can use OpenCL for Leapfrog (collisions — not yet). Rendering is done on GPU using [`vello`](https://github.com/linebender/vello). 
+Currently uses 4th order Leapfrog integrator with Yoshida coefficients and preserves momentum on collisions if `restitution_coefficient = 1` (see config.toml). Can use OpenCL for Leapfrog and broad phase collision detection. Rendering is done on GPU using [`vello`](https://github.com/linebender/vello).