clarify that Database::put_* methods overwrite the previous

value

heed/src/database.rs

@@ -1787,7 +1787,8 @@ impl<KC, DC, C> Database<KC, DC, C> {
  RwCursor::new(txn, self.dbi).map(|cursor| RwRevPrefix::new(cursor, prefix_bytes))
  }
 
- /// Insert a key-value pair in this database. The entry is written with no specific flag.
+ /// Insert a key-value pair in this database, replacing any previous value. The entry is
+ /// written with no specific flag.
  ///
  /// ```
  /// # use std::fs;
@@ -1842,7 +1843,8 @@ impl<KC, DC, C> Database<KC, DC, C> {
  Ok(())
  }
 
- /// Insert a key-value pair where the value can directly be written to disk.
+ /// Insert a key-value pair where the value can directly be written to disk, replacing any
+ /// previous value.
  ///
  /// ```
  /// # use std::fs;
@@ -1908,7 +1910,8 @@ impl<KC, DC, C> Database<KC, DC, C> {
  }
  }
 
- /// Insert a key-value pair in this database. The entry is written with the specified flags.
+ /// Insert a key-value pair in this database, replacing any previous value. The entry is
+ /// written with the specified flags.
  ///
  /// ```
  /// # use std::fs;