raft: add example in Log documentation

src/raft/log.rs

@@ -50,7 +50,16 @@ impl encoding::Key<'_> for KeyPrefix {}
 /// are replicated across nodes and applied sequentially to the local state
 /// machine. Each entry contains an index, command, and the term in which the
 /// leader proposed it. Commands may be noops (None), which are added when a
-/// leader is elected (see section 5.4.2 in the Raft paper).
+/// leader is elected (see section 5.4.2 in the Raft paper). For example:
+///
+/// Index | Term | Command
+/// ------|------|------------------------------------------------------
+/// 1 | 1 | None
+/// 2 | 1 | CREATE TABLE table (id INT PRIMARY KEY, value STRING)
+/// 3 | 1 | INSERT INTO table VALUES (1, 'foo')
+/// 4 | 2 | None
+/// 5 | 2 | UPDATE table SET value = 'bar' WHERE id = 1
+/// 6 | 2 | DELETE FROM table WHERE id = 1
 ///
 /// A key/value store is used to store the log entries on disk, keyed by index,
 /// along with a few other metadata keys (e.g. who we voted for in this term).