Mention wide-column support in HISTORY.md (#10959)

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/10959

Reviewed By: akankshamahajan15

Differential Revision: D41348198

Pulled By: ltamasi

fbshipit-source-id: 51e89d03c1fe87f576a766f609a7f233a519c83d

HISTORY.md

@@ -14,6 +14,7 @@
 ### New Features
 * Add basic support for user-defined timestamp to Merge (#10819).
 * Add stats for ReadAsync time spent and async read errors.
+* Basic support for the wide-column data model is now available. Wide-column entities can be stored using the `PutEntity` API, and retrieved using `GetEntity` and the new `columns` API of iterator. For compatibility, the classic APIs `Get` and `MultiGet`, as well as iterator's `value` API return the value of the anonymous default column of wide-column entities; also, `GetEntity` and iterator's `columns` return any plain key-values in the form of an entity which only has the anonymous default column. `Merge` (and `GetMergeOperands`) currently also apply to the default column; any other columns of entities are unaffected by `Merge` operations. Note that some features like compaction filters, transactions, user-defined timestamps, and the SST file writer do not yet support wide-column entities; also, there is currently no `MultiGet`-like API to retrieve multiple entities at once. We plan to gradually close the above gaps and also implement new features like column-level operations (e.g. updating or querying only certain columns of an entity).
 
 ### Public API Changes
 * Marked `block_cache_compressed` as a deprecated feature. Use SecondaryCache instead.