fix typo in regulated pure pursuit readme (#2228)

nav2_regulated_pure_pursuit_controller/README.md

@@ -4,7 +4,7 @@ This is a controller (local trajectory planner) that implements a variant on the
 
 Code based on a simplified version of this controller is referenced in the [Writing a New Nav2 Controller](https://navigation.ros.org/plugin_tutorials/docs/writing_new_nav2controller_plugin.html) tutorial.
 
-This plugin implements the `nav2_core::Controller` interface allowing it to be used acros the navigation stack as a local trajectory planner in the controller server's action server (`controller_server`).
+This plugin implements the `nav2_core::Controller` interface allowing it to be used across the navigation stack as a local trajectory planner in the controller server's action server (`controller_server`).
 
 It builds on top of the ordinary pure pursuit algorithm in a number of ways. It also implements all the common variants of the pure pursuit algorithm such as adaptive pure pursuit. This controller is suitable for use on all types of robots, including differential, legged, and ackermann steering vehicles. It may also be used on omni-directional platforms, but won't be able to fully leverage the lateral movements of the base (you may consider DWB instead).