Update installation.rst

[yakky]

Description

Describe:

Update installation with reference to django CMS documentation and videos to help first time users to getting familiar with django CMS concepts

References

Link tp #524

Checklist

• I have read the contribution guide
• Code lint checked via inv lint
• changes file included (see docs)
• Usage documentation added in case of new features
• Tests added N/A

[codecov]

Codecov Report

Merging #635 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #635   +/-   ##
========================================
  Coverage    94.50%   94.50%           
========================================
  Files           22       22           
  Lines         1111     1111           
  Branches       138      138           
========================================
  Hits          1050     1050           
  Misses          23       23           
  Partials        38       38           

Flag	Coverage Δ
#unittests	94.50% <ø> (ø)

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[coveralls]

Coverage remained the same at 96.74% when pulling 4c0c420 on docs/issue-524-first-use into 12a2141 on develop.

[yakky]

Content included in #631