docs: fix and clarify podman usage instructions

[rugk]

• the full reference jbarlow83/ocrmypdf-alpine (and new tag) as in the other commands may fix an issue if you do not have ocrmypdf already downloaded locally
• also clarified the command at the end for usage when SELinux is enabled
• also removed one superfluous space

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.89%. Comparing base (9dbce33) to head (d90b7ae).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1601   +/-   ##
=======================================
  Coverage   88.89%   88.89%           
=======================================
  Files          96       96           
  Lines        7192     7192           
  Branches      736      736           
=======================================
  Hits         6393     6393           
  Misses        597      597           
  Partials      202      202           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.