[Devtools Week] Fix book of appstudio link

[thepetk]

What does this PR do?:

Simply fixes a broken link to book of appstudio (currently gives 404) with a working one (https://redhat-appstudio.github.io/architecture/ref/index.html)

Which issue(s)/story(ies) does this PR fixes:

N/A - Part of devtools week

PR acceptance criteria:

• Unit/Functional tests

• Documentation

• Client Impact

How to test changes / Special notes to the reviewer:

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.63%. Comparing base (4863efd) to head (4778e83).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #448      +/-   ##
==========================================
+ Coverage   80.57%   80.63%   +0.05%     
==========================================
  Files          35       35              
  Lines        5040     5040              
==========================================
+ Hits         4061     4064       +3     
+ Misses        774      772       -2     
+ Partials      205      204       -1     

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[michael-valdron]

/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: michael-valdron, thepetk

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