Clarify the use of `buildEnv` in deploy.js
Clarify the use of `buildEnv` in deploy.js

Setting `buildEnv` to `development` makes no sense and is considered harmful.
Added reasoning behind this statement to the README and warn people of doing this.
kevinlondon/ember-deploy-s3,he9qi/ember-deploy-s3,he9qi/ember-deploy-s3,LevelbossMike/ember-deploy-s3,kevinlondon/ember-deploy-s3,LevelbossMike/ember-deploy-s3