Add Google Play badge to Readme for #14794

[yoasif]

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

To download an APK when reviewing a PR:

1. click on Show All Checks,
2. click Details next to "Taskcluster (pull_request)" after it appears and then finishes with a green checkmark,
3. click on the "Fenix - assemble" task, then click "Run Artifacts".
4. the APK links should be on the left side of the screen, named for each CPU architecture

[firefoxci-taskcluster]

No Taskcluster jobs started for this pull request

The `allowPullRequests` configuration for this repository (in `.taskcluster.yml` on the
default branch) does not allow starting tasks for this pull request.

[pocmo]

👍

[codecov-commenter]

Codecov Report

Merging #14829 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master   #14829      +/-   ##
============================================
- Coverage     29.77%   29.76%   -0.02%     
- Complexity     1165     1166       +1     
============================================
  Files           447      447              
  Lines         18135    18135              
  Branches       2355     2355              
============================================
- Hits           5399     5397       -2     
- Misses        12359    12361       +2     
  Partials        377      377              

Impacted Files	Coverage Δ	Complexity Δ
...mponents/searchengine/FenixSearchEngineProvider.kt	62.16% <0.00%> (-1.81%)	14.00% <0.00%> (+1.00%)	⬇️

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