Update resource restrictions

* 512MB is a strongly recommended limit for Docker image size, but isn't strictly enforced, and isn't always feasible. The previous 256MB was too low. I've updated the limit, and changed "must" to "should".
* Our default memory limit is also higher now, but is a strict limit. I've updated the memory limit.
* Fix some typos.

cc @mrb @codeclimate/review

Author: wfleming

SPEC.md

@@ -296,8 +296,8 @@ Your `Docker` image must be built with the name `codeclimate/codeclimate-YOURENG
 In order to ensure analysis runs reliably across a variety of systems, Engines
 must conform to some basic resource restrictions:
 
-* The Docker image for an Engine must not exceed 250MB, including all layers
-* The combined total RSS memory usage my all processes within the Docker container must not exceed 256MB at any time.
+* The Docker image for an Engine must not exceed 512MB, including all layers.
+* The combined total RSS memory usage by all processes within the Docker container must not exceed 1GB at any time.
 * All Engines must complete and exit within 10 minutes.
 
 ## Security Restrictions