[doc/book/devweb/ajax] warning about deprecated use of ajax

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branch : 3.27

doc/book/devweb/ajax.rst

@@ -3,6 +3,17 @@
 Ajax
 ----
 
+.. warning::
+
+    This approach is deprecated in favor of using
+    `cwclientlibjs <https://www.npmjs.com/package/@logilab/cwclientlibjs>`_.
+    If your use react for your UI, try the react components from the
+    `cwelements <https://www.npmjs.com/package/@logilab/cwelements>`_ library.
+    The documentation is kept here as reference.
+
+    For historical reference of what Ajax is and used to be, one can read the
+    `wikipedia article about Ajax <https://en.wikipedia.org/wiki/Ajax_(programming)>`_.
+
 CubicWeb provides a few helpers to facilitate *javascript <-> python* communications.
 
 You can, for instance, register some python functions that will become