Update tasks for deploying sandbox app (#255)

* Add a readme to the sandbox template

It's good to explain what the repo actually is

* Update Rake task for deploying sandbox app

- Bunder.with_clean_env is deprecated. I'm not sure if
  `with_unbundled_env` is the correct option, but it seems to do the
  job.
- Use SSL version of git clone to avoid having to use a username and
  password. SSL makes sense if deploying from the local machine: maybe
  at some point this was deployed automatically, but I can't see any
  trace of that.
- Temporarily lock to building on the latest Rails 5 version: the
  sandbox app is locked to use Rails 5, and Godmin isn't very well
  supported on Rails 6 yet.

Rakefile

@@ -36,14 +36,14 @@ namespace :sandbox do
   task :deploy do
     message = "Generated from: https://github.com/varvet/godmin/commit/#{`git rev-parse HEAD`.strip}"
     template_path = File.expand_path("../template.rb", __FILE__)
-    Bundler.with_clean_env do
+    Bundler.with_unbundled_env do
       Dir.mktmpdir do |dir|
         Dir.chdir(dir)
-        system("git clone https://github.com/varvet/godmin-sandbox.git")
+        system("git clone git@github.com:varvet/godmin-sandbox.git")
         if $CHILD_STATUS.success?
           Dir.chdir("godmin-sandbox")
           system("rm -rf *")
-          system("rails new . -d postgresql -m #{template_path} --without-engine --skip-spring")
+          system("rails _5.2.5_ new . -d postgresql -m #{template_path} --without-engine --skip-spring")
           if $CHILD_STATUS.success?
             system("git add --all")
             system("git commit -m '#{message}'")

template.rb

@@ -21,6 +21,7 @@ def install_standalone
     modify_author_service
     modify_article_controller
     modify_article_service
+    modify_readme
 
     migrate_and_seed
   end
@@ -64,6 +65,7 @@ def install_engine
     modify_author_service("admin")
     modify_article_controller("admin")
     modify_article_service("admin")
+    modify_readme
 
     migrate_and_seed
   end
@@ -308,6 +310,18 @@ def batch_action_destroy(authors)
   end
 end
 
+def modify_readme
+  readme_file = "README.md"
+  run "rm #{readme_file}"
+  readme_text = <<~README
+    # README
+
+    This is the source code for a demo application of the [Godmin](https://github.com/varvet/godmin) admin framework for Rails.
+    It is generated by running `rake sandbox:deploy` inside the Godmin repo.
+  README
+  File.open(readme_file, 'w') { |file| file.write(readme_text) }
+end
+
 def migrate_and_seed
   rake("db:migrate")
   rake("db:seed")