* [doc] Fix document around categorical parameters. [skip ci] * note on validate parameter [skip ci] * Fix dask doc as well [skip ci]
The documentation of xgboost is generated with recommonmark and sphinx. You can build it locally by typing "make html" in this folder. Checkout https://recommonmark.readthedocs.org for guide on how to write markdown with extensions used in this doc, such as math formulas and table of content.