docs(readme): add Advertisement component to list

[layershifter]

We forgot to do this in #1292.

[codecov-io]

Codecov Report

Merging #1421 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1421      +/-   ##
==========================================
+ Coverage   99.74%   99.75%   +<.01%     
==========================================
  Files         141      140       -1     
  Lines        2354     2402      +48     
==========================================
+ Hits         2348     2396      +48     
  Misses          6        6

Impacted Files	Coverage Δ
src/modules/Accordion/AccordionContent.js	100% <0%> (ø)	✅
src/collections/Form/FormField.js	100% <0%> (ø)	✅
src/modules/Dropdown/Dropdown.js	100% <0%> (ø)	✅
src/views/Card/Card.js	100% <0%> (ø)	✅
src/modules/Search/Search.js	100% <0%> (ø)	✅
src/modules/Modal/ModalHeader.js	100% <0%> (ø)	✅
src/modules/Dropdown/DropdownMenu.js	100% <0%> (ø)	✅
src/modules/Accordion/AccordionTitle.js	100% <0%> (ø)	✅
src/collections/Form/FormTextArea.js	100% <0%> (ø)	✅
src/modules/Modal/ModalActions.js	100% <0%> (ø)	✅
... and 24 more

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