cmovnz and cmovz docs are confusing

[elahn]

In the description of both cmovnz and cmovz, it says:

conditionally moves value to self when condition is equal to zero.

The function names and first line of description convey their purpose. In the rest, it might be more clear to separate the function behaviour from instructions used to implement it.

The crate-level docs are excellent. Thank you for publishing the cmov crate! Implementing branch-free algorithms in Rust are no longer blocked on learning inline assembly.

[tarcieri]

Does #991 address your concerns?