docs(examples): demo apps setup

[Matii96]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What has been added?

Examples of unifig usages with express and Nest.js.

[codecov-commenter]

Codecov Report

Merging #17 (13dd122) into main (585b3c5) will increase coverage by 0.08%.
The diff coverage is 97.61%.

@@            Coverage Diff             @@
##             main      #17      +/-   ##
==========================================
+ Coverage   97.76%   97.85%   +0.08%     
==========================================
  Files          34       34              
  Lines         358      373      +15     
  Branches       65       69       +4     
==========================================
+ Hits          350      365      +15     
  Misses          8        8              

Flag	Coverage Δ
unittests	97.85% <97.61%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...lib/adapters/class-adapters/plain/plain.adapter.ts	100.00% <ø> (ø)
packages/nest/lib/config.module.ts	84.21% <85.71%> (+2.96%)	⬆️
...kages/core/lib/loader/decorators/from.decorator.ts	100.00% <100.00%> (ø)
...ges/core/lib/loader/decorators/nested.decorator.ts	100.00% <100.00%> (ø)
packages/core/lib/loader/loader.impl.ts	100.00% <100.00%> (ø)
...kages/core/lib/manager/container/container.impl.ts	100.00% <100.00%> (ø)
packages/core/lib/manager/manager.impl.ts	97.36% <100.00%> (+0.07%)	⬆️
...core/lib/manager/source-group/source-group.impl.ts	100.00% <100.00%> (ø)
...ages/core/lib/validator/errors/validation.error.ts	100.00% <100.00%> (ø)
packages/core/lib/validator/validator.impl.ts	95.55% <100.00%> (+0.20%)	⬆️
... and 3 more