Document how to switch between stable release and upstream dev/platform

scripts/docspregen.py

@@ -290,6 +290,32 @@ Examples are listed from `%s development platform repository <%s>`_:
             generate_debug_boards(
                 compatible_boards, skip_columns=["Platform"]))
 
+    #
+    # Development version of dev/platform
+    #
+    lines.append("""
+Stable and upstream versions
+----------------------------
+
+You can switch between `stable releases <https://github.com/platformio/platform-{name}/releases>`__
+of {title} development platform and the latest upstream version using
+:ref:`projectconf_env_platform` option as described below:
+
+.. code-block:: ini
+
+    ; Custom stable version
+    [env:stable]
+    platform ={name}@x.y.z
+    board = ...
+    ...
+
+    ; The latest upstream/development version
+    [env:upstream]
+    platform = https://github.com/platformio/platform-{name}.git
+    board = ...
+    ...
+""".format(name=p.name, title=p.title))
+
     #
     # Packages
     #