Add TileDB Embedded Note to HISTORY.md
# TileDB-Py 0.12.0 Release Notes
+## TileDB Embedded updates:
+* TileDB-Py 0.12.0 includes TileDB Embedded [TileDB 2.6.0](https://github.com/TileDB-Inc/TileDB/releases/tag/2.6.0)
+
## API Changes
* Allow writing to dimension-only array (zero attributes) by using assignment to `None`, for example: `A[coords] = None` (given `A: tiledb.Array`) [#854](https://github.com/TileDB-Inc/TileDB-Py/pull/854)
* Remove repeating header names for `attr` when displaying `ArraySchema` in Jupyter Notebooks [#856](https://github.com/TileDB-Inc/TileDB-Py/pull/856)
