Add smoke test of README example

[codecov[bot]]

Codecov Report

Merging #13 (9ec7990) into main (f129326) will increase coverage by 51.90%. The diff coverage is n/a.

@@             Coverage Diff             @@
##             main      #13       +/-   ##
===========================================
+ Coverage   29.05%   80.96%   +51.90%     
===========================================
  Files          10       10               
  Lines         499      499               
  Branches      104      104               
===========================================
+ Hits          145      404      +259     
+ Misses        349       69      -280     
- Partials        5       26       +21     

Flag	Coverage Δ
back-end	100.00% <ø> (ø)
front-end	80.24% <ø> (+53.84%)	:arrow_up:

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Impacted Files	Coverage Δ
js/jupyterlab-deck/src/manager.ts	80.55% <0.00%> (+51.11%)	:arrow_up:
js/jupyterlab-deck/src/notebook/presenter.ts	74.03% <0.00%> (+67.30%)	:arrow_up:
js/jupyterlab-deck/src/notebook/extension.ts	100.00% <0.00%> (+75.00%)	:arrow_up:
js/jupyterlab-deck/src/remote.tsx	86.20% <0.00%> (+82.75%)	:arrow_up:

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