Document the enchant dependency for building docs

[tim-schilling]

The sphinxcontrib-spelling library depends on pyenchant which depends on the Enchant library being installed.

Perhaps we modify the writing documentation section to have a prequisites section that @okotdaniel has suggested in the past. It should indicate the person needs the Enchant library installed and we can link to pyenchant's install documentation.

[JohananOppongAmoateng]

@tim-schilling would love to work on this

[tim-schilling]

Sounds good, thank you @JohananOppongAmoateng