doc: update comments in the faceted search example

[DawChihLiou]

This PR replaces the incorrect comment copied from the basic example with an explanation that describes the faceted search example.

[codecov-commenter]

Codecov Report

Merging #1737 (28058ae) into main (7385a8f) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1737   +/-   ##
=======================================
  Coverage   94.13%   94.14%           
=======================================
  Files         266      267    +1     
  Lines       50814    50903   +89     
=======================================
+ Hits        47835    47921   +86     
- Misses       2979     2982    +3     

Impacted Files	Coverage Δ
fastfield_codecs/src/null_index/sparse.rs	95.46% <0.00%> (-1.29%)	⬇️
stacker/src/expull.rs	98.33% <0.00%> (-0.56%)	⬇️
common/src/lib.rs	89.33% <0.00%> (ø)
fastfield_codecs/src/lib.rs	98.89% <0.00%> (ø)
common/src/group_by.rs	100.00% <0.00%> (ø)
fastfield_codecs/src/null_index/dense.rs	99.16% <0.00%> (+0.10%)	⬆️
src/indexer/segment_updater.rs	95.44% <0.00%> (+0.13%)	⬆️
src/schema/schema.rs	98.91% <0.00%> (+0.13%)	⬆️
fastfield_codecs/src/monotonic_mapping.rs	100.00% <0.00%> (+2.52%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[fulmicoton]

Can you fix the formatting? (Running make fmt should do the job) @DawChihLiou

[DawChihLiou]

@fulmicoton Thanks for reviewing! I've formatted the change:)