DOC: add user guide on xgboost

[traderbxy]

What do these changes do?

add xgboost.rst at doc/source/libraries/xorbits_train by following the code style on doc/source/libraries/xorbits_data/numpy.rst

Related issue number

713

[codecov[bot]]

Codecov Report

Merging #754 (e8951f5) into main (e77db37) will increase coverage by 3.75%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #754      +/-   ##
==========================================
+ Coverage   89.84%   93.59%   +3.75%     
==========================================
  Files        1059     1059              
  Lines       79781    79781              
  Branches    16504    16504              
==========================================
+ Hits        71676    74668    +2992     
+ Misses       6262     3435    -2827     
+ Partials     1843     1678     -165     

Flag	Coverage Δ
unittests	93.48% <ø> (+3.75%)	:arrow_up:

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

see 122 files with indirect coverage changes