Add documentation for schemas

[snuyanzin]

fixes #498

cc @panilya since you've asked about it

[codecov-commenter]

Codecov Report

Merging #533 (7355c1f) into main (2d6ebd5) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

❗ Current head 7355c1f differs from pull request most recent head 95f4a67. Consider uploading reports for the commit 95f4a67 to get more accurate results

@@             Coverage Diff              @@
##               main     #533      +/-   ##
============================================
- Coverage     91.91%   91.85%   -0.06%     
+ Complexity     2359     2358       -1     
============================================
  Files           247      247              
  Lines          4948     4949       +1     
  Branches        530      530              
============================================
- Hits           4548     4546       -2     
+ Misses          272      270       -2     
- Partials        128      133       +5     

Impacted Files	Coverage Δ
.../net/datafaker/transformations/CsvTransformer.java	96.66% <100.00%> (+0.05%)	⬆️
...ker/idnumbers/pt/br/IdNumberGeneratorPtBrUtil.java	92.59% <0.00%> (-3.71%)	⬇️
.../datafaker/transformations/sql/SqlTransformer.java	86.29% <0.00%> (-0.75%)	⬇️
.../main/java/net/datafaker/service/FakerContext.java	87.17% <0.00%> (+2.56%)	⬆️

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