feat(control, flow, sense): docs

[vovacha]

• control, flow, sense: add docs
• sense: rename account -> account_id

Not sure if the docs for storage are not too verbose.
I followed the next example from Acala:

/// Session points for each candidate.
///
/// SessionPoints: map AccountId => u32
#[pallet::storage]
#[pallet::getter(fn session_points)]
pub type SessionPoints<T: Config> = StorageMap<_, Twox64Concat, T::AccountId, u32, ValueQuery>;