Improve documentation descriptions of how to use SAT solvers

[wkschwartz]

• The package documentation is unhelpful.
• The documentation for Literal is unhelpful
• Option documentation refers to Picosat functions.
• The documentation for AddClauses is wrong

[wkschwartz]

Commits 2317237, dbd2d31, 7a26042, 2f73a04 close this issue.