update categorical encoding user guide

[gurjinderbassi]

Updated the categorical encoding introduction section in the User Guide. It includes an introduction to categorical encoding, its importance and briefly explains different encoding methods supported by Feature-engine.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.18%. Comparing base (a347bc8) to head (15aa8f2).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #758   +/-   ##
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  Coverage   98.18%   98.18%           
=======================================
  Files         105      105           
  Lines        4074     4074           
  Branches      795      795           
=======================================
  Hits         4000     4000           
  Misses         29       29           
  Partials       45       45           

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[VascoSch92]

Suggested change

	log( p(X=xj|Y = 1) / p(X=xj|Y=0) )
	log( p(X=x_j|Y = 1) / p(X=x_j|Y=0) )

or?

[solegalli]

Thank you @gurjinderbassi ! Great work with this massive doc update :)

I'll add your contribution to the next release. The docs will be live in the next 20 minutes :)