Fix dead link in installation and usage docs

[saschagrunert]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

The link does not exist, so we now link to the "Constrain spod scheduling" section.

Which issue(s) this PR fixes:

None

Does this PR have test?

None

Special notes for your reviewer:

None

Does this PR introduce a user-facing change?

Updated dead documentation link on how to constrain the spod to specific nodes.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 41.27%. Comparing base (11d77f4) to head (602e6af).
Report is 211 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2266      +/-   ##
==========================================
- Coverage   45.50%   41.27%   -4.23%     
==========================================
  Files          79      109      +30     
  Lines        7782    15653    +7871     
==========================================
+ Hits         3541     6461    +2920     
- Misses       4099     8724    +4625     
- Partials      142      468     +326     

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ccojocar, saschagrunert

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[ccojocar]

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