Update 6.1-to-6.2.md

Added a few enters so markdown can process the code (without adding bash in front of it)

Minor grammatical updates in some of the labels.

Add specs for NotificationsHelper

corrected the url of the init-script

Use init.d/gitlab script from 6-0-stable branch

Seems like init.d/gitlab script from master branch is not working anymore. Change to a version from 6-0-stable works fine.

It says:
```
Starting the GitLab Unicorn web server...
/etc/init.d/gitlab: 132: /etc/init.d/gitlab: script/web: not found
Starting the GitLab Sidekiq event dispatcher...
/etc/init.d/gitlab: 141: /etc/init.d/gitlab: script/background_jobs: not found
GitLab is not running.
```

Show milestones iid instead of id

Refactor search_autocomplete_source

Add logrotate config to update docs