docs: Add the list of things still left for V1

[teolemon]

What

• Add the list of things still left for V1 to the README. Feel free to comment here.
• For reference, the exact list blocking issues board is located at : https://github.com/orgs/openfoodfacts/projects/7/views/6

Part of

• Launch improved app

[codecov-commenter]

Codecov Report

Merging #1636 (1148ae1) into develop (2ea0da3) will decrease coverage by 1.33%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           develop   #1636      +/-   ##
==========================================
- Coverage     8.86%   7.52%   -1.34%     
==========================================
  Files          161     190      +29     
  Lines         6623    9367    +2744     
==========================================
+ Hits           587     705     +118     
- Misses        6036    8662    +2626     

Impacted Files	Coverage Δ
...kages/smooth_app/lib/widgets/attribute_button.dart	0.00% <0.00%> (-92.00%)	⬇️
...s/smooth_app/lib/data_models/user_preferences.dart	8.73% <0.00%> (-23.57%)	⬇️
packages/smooth_app/lib/themes/smooth_theme.dart	60.00% <0.00%> (-22.98%)	⬇️
...p/lib/generic_lib/dialogs/smooth_alert_dialog.dart	15.11% <0.00%> (-19.10%)	⬇️
...mooth_app/lib/data_models/product_preferences.dart	24.65% <0.00%> (-6.78%)	⬇️
.../smooth_app/lib/pages/onboarding/welcome_page.dart	0.00% <0.00%> (-3.13%)	⬇️
packages/smooth_app/lib/main.dart	14.91% <0.00%> (-2.99%)	⬇️
.../smooth_app/lib/pages/onboarding/scan_example.dart	0.00% <0.00%> (-2.28%)	⬇️
...p/lib/pages/onboarding/consent_analytics_page.dart	0.00% <0.00%> (-1.57%)	⬇️
...smooth_app/lib/pages/product/new_product_page.dart	0.00% <0.00%> (-0.88%)	⬇️
... and 183 more

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[M123-dev]

Should we merge or close since v1 is out

[teolemon]

yes, there's v1.1 priorities @M123-dev