Add warning on production env

Author: mrcasals

README.md

@@ -7,7 +7,9 @@ An opinionated Rails generator to configure your [`decidim`](https://github.com/
 Add this gem to your Gemfile:
 
 ```ruby
-gem "decidim-deploy-heroku", git: "https://github.com/codegram/decidim-deploy-heroku.git"
+group :development do
+  gem "decidim-deploy-heroku", git: "https://github.com/codegram/decidim-deploy-heroku.git"
+end
 ```
 
 Run `bundle install` and then run the gem generator:
@@ -16,3 +18,9 @@ Run `bundle install` and then run the gem generator:
 bundle install
 bundle exec rails g decidim:deploy:heroku_installer
 ```
+
+Once the last command is performed you can uninstall the gem by removing it from the `Gemfile` and rerun `bundle install`. 
+
+### Problems on production
+
+This gem is not supposed to be deployed to a production environment and might fail. See [\#3](https://github.com/codegram/decidim-deploy-heroku/issues/3) for an example of this problem. If you encounter this problem, make sure you have removed the gem for the `Gemfile` and rerun `bundle install` to copletely remove it from the bundle.