Documentation for public functions

[tolikzinovyev]

Why

We should have proper documentation for each public function before presenting the library.

What

See https://github.com/cardano-scaling/alba/pull/63/files#r1837559375.

 /// Adds two numbers together.
///
/// # Arguments
///
/// * `a` - The first integer to add.
/// * `b` - The second integer to add.
///
/// # Returns
///
/// An integer that is the sum of `a` and `b`.
///
/// # Examples
///
/// ```
/// let result = add(2, 3);
/// assert_eq!(result, 5);
/// ```