Update HISTORY.rst

HISTORY.rst

@@ -16,6 +16,7 @@ Release History
 - The light format uses ``# + [markdown]`` rather than the previous ``cell_type`` metadata to identify markdown cells with metadata (#356)
 - Explicit Markdown cells in the light format ``# + [markdown]`` can use triple quotes (#356)
 - Cell metadata can be encoded as either key=value (the new default) or in JSON. An automatic option ``cell_metadata_json`` should help minimize the impact on existing files (#344)
+- R Markdown hidden inputs, outputs, or cells are now mapped to the corresponding Jupyter Book tags by default (#337)
 - The Jupyter Notebook extension for Jupytext is compatible with Jupyter Notebook 6.0 (#346)
 - ``jupytext notebook.py --to ipynb`` updates the timestamp of ``notebook.py`` so that the paired notebook still works in Jupyter (#335, #254)
 - Added support for Rust/Evxcr, by Jonas Bushart (#351)