Update the On-boarding Course

This PR is intended to reflect the collected feedback on the OnBoarding course.

Changes to be made:

• Add section to onboarding course about picking tasks for sprints. The section should describe:
  • How/when team members pick tasks for sprints.
  • What one should do for the first few sprints when one does not have sufficient information to pick tasks on their own.
• Some „client handling“ guidelines could help, e.g. to say how to react to help@, how to calm clients, how to add tasks, etc.
• Add a link to https://www.remoteonly.org/ somewhere in the onboarding.
• While reading the "Ticket statuses" section on the onboarding course I noticed there is an additional column "Recurring" on the JIRA board which is not mentioned here. Could we add a small description for this column? See public!10 (merged)
• Update something's down documentation to include this details about OVH vip line: See https://gitlab.com/opencraft/documentation/private/merge_requests/311
• Mention at the beginning of the course that there are links to various resources in GitHub/GitLab repositories under the open-craft organization which give a 404 Not Found error unless the user is signed into GitHub/GitLab.
• The Course discovery service - Getting started guide link mentioned in https://github.com/open-craft/documentation/blob/master/devstack_setup.md is not valid and throws a 404 error.
• The link to the Ticket statuses page in this page is not valid and throws a 404 error.
• In the edX XBlock creation tutorial, the database migrations fail because the expected var directory doesn't exist and the instructions fail to specify that the directory has to be created.
• There is an invalid python interpreter command - python no mentioned in this page of the XBlock tutorial.
• The on-boarding course has a link to setting up the edX devstack but doesn't mention if it is necessary to setup the analytics stack (the instructions for which are on the same page) as well.
• Get course content search working in the Onboarding course. cf Enabling Open edX Search.
• Section "Time management and invoices > Time management", in Question #2 (closed), issue OC-515 can be linked to its url.
• Section "OpenCraft > Coding Standards" Code Review Guidelines & Gotchas PDF, contains a number of broken links, and confusing information (e.g. What is TNL?)