Document how to use Pry

Procfile.example

@@ -4,6 +4,7 @@ postgresql: support/postgresql-signal-wrapper postgres -D /home/git/postgresql/d
 #openldap: cd gitlab-openldap && libexec/slapd -F slapd.d -d2 -h "ldap://127.0.0.1:3890"
 gitlab-workhorse: PATH=/home/git/gitlab-workhorse:$PATH gitlab-workhorse -authSocket /home/git/gitlab.socket -listenAddr $host:$port -documentRoot /home/git/gitlab/public -developmentMode
 rails-web: RAILS_ENV=development support/exec-cd gitlab bin/web start_foreground
+#rails-web: RAILS_ENV=development support/exec-cd gitlab bundle exec thin --socket=/home/git/gitlab.socket start
 rails-background-jobs: SIDEKIQ_LOG_ARGUMENTS=1 RAILS_ENV=development support/exec-cd gitlab bin/background_jobs start_foreground
 #influxdb: influxdb/bin/influxd -config influxdb/influxdb.conf
 #grafana: support/wait-postgresql-ready support/exec-cd grafana bin/grafana-server -config grafana.ini

doc/howto/pry.md

+# Debugging with Pry
+
+[Pry](http://pryrepl.org/) allows you to set breakpoints in Ruby code
+for interactive debugging. Just drop in the magic word `binding.pry`.
+
+When running tests Pry's interactive debugging prompt appears in the
+terminal window where you start your test command (`rake`, `rspec`
+etc.).
+
+If you want to get a debugging prompt while browsing on your local
+development server (localhost:3000) you need to make a change to the
+Procfile in your GDK root directory because Unicorn is not compatible
+with Pry.
+
+There are two `rails-web` lines in the Procfile, one containing
+`bin/web` and one containing `thin`. Comment out the line containing
+`bin/web` and uncomment the line containing `thin`. Now when you start
+GDK with `./run` or `./run app` the Rails web application runs in Thin
+instead of Unicorn.

[username-removed-742366]

Hey thanks @jacobvosmaer-gitlab , in my case I also had to add these into the Gemfile:

group :development, :test do
  gem 'pry'
  gem 'rb-readline'
end