Add simple doc for context module
* limitations under the License.
* -----------------------------------------------------------------------------
*/
+//! Transaction context management.
+//!
+//! In Transact, state reads and writes are scoped (sandboxed) to a specific "context" that
+//! contains a reference to a state ID (such as a Merkle-Radix state root hash) and one or more
+//! previous contexts. The context manager implements the context lifecycle and services the calls
+//! that read, write, and delete data from state.
/// Unique id that references a "Context" from which a `Transaction` can query state and
/// modify events, data, and state.
