Document how to document pythonizations

Author: enirolf

_data/navigation.yml

@@ -158,6 +158,8 @@ for_developers:
         url: for_developers/docs/guidelines
       - title: Running Doxygen locally
         url: for_developers/docs/local_doxygen
+      - title: Documenting ROOT Pythonizations
+        url: for_developers/docs/pythonizations
       - title: Useful tips
         url: for_developers/docs/useful_tips
    - title: Editing the ROOT website

for_developers/docs/pythonizations.md

@@ -0,0 +1,33 @@
+---
+title: Documenting ROOT Pythonizations
+layout: single
+toc: no
+toc_sticky: no
+sidebar:
+  nav: "for_developers"
+---
+
+Some ROOT classes have *pythonizations* that require additional documentation. These can be added as special boxes to the rendered Doxygen page of their corresponding C++ class. As an example, see the Python-specific [RDataFrame](https://root.cern/doc/master/classROOT_1_1RDataFrame.html#python) docs. This documentation is written in the pythonization files corresponding to the original C++ class, which can be found in `<root_sources>/bindings/pyroot/pythonizations/python/ROOT/_pythonization`. Documentation is added as a module-level docstring, which should following the template below, replacing `{CLASS_NAME}` with the corresponding C++ class name, `{BLOCK_TITLE}` with the title of the documentation block (in most cases, "PyROOT" is used) and `{DOCUMENTATION_BODY}` with the documentation body, which supports the usual Doxygen tags and other formatting methods (see also the [documentation formatting tips](../useful_tips)).
+
+```
+r"""
+/**
+\class {CLASS_NAME}
+\brief \parblock \endparblock
+\htmlonly
+<div class="pyrootbox">
+\endhtmlonly
+\anchor python
+
+## {BLOCK_TITLE}
+
+{DOCUMENTATION_BODY}
+
+\htmlonly
+</div>
+\endhtmlonly
+*/
+"""
+```
+
+The `\anchor` tag adds a permalink to the PyROOT box on rendered documentation page, allowing for easy linking to the Python-specific documentation by appending `#python` to the URL of the doxygen page (i.e., [https://root.cern/doc/master/classROOT_1_1RDataFrame.html#python](https://root.cern/doc/master/classROOT_1_1RDataFrame.html#python)).