Add a buildcfg/readme.md

buildcfg/readme.md

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+# Build configs
+
+This directory includes configuration files (json) for the tasks/build.js
+build script.
+
+Notes:
+
+`use_types_for_optimization` is set to `false` for the SIMPLE and WHITESPACE
+builds.  If it was set to `true` we would get function names like
+`ol_control_Control_prototype$setMap` in the compiled code when using the
+SIMPLE compilation. `use_types_for_optimization` is only appropriate for
+ADVANCED compilation. To be sure we also don't set it for WHITESPACE.