Add (temporary?) docs page for #275 work items

doc/conf.py

@@ -169,6 +169,12 @@ def setup(app: "sphinx.application.Sphinx") -> None:
     "pull": ("https://github.com/iiasa/message-ix-models/pull/%s", "PR #%s"),
     "gh-user": ("https://github.com/%s", "@%s"),
     "source": ("https://github.com/iiasa/message-ix-models/blob/main/%s", "%s"),
+    # Temporary, for #275. DO NOT use these except in doc/dev/275.rst
+    "md-to-migrate": ("https://github.com/iiasa/message_data/blob/ssp_dev/%s", None),
+    "msc-to-migrate": (
+        "https://github.com/iiasa/message_single_country/blob/SSP_Dev_2023/%s",
+        None,
+    ),
 }
 
 # -- Options for sphinx.ext.intersphinx ------------------------------------------------

doc/dev/275.rst

@@ -0,0 +1,46 @@
+Summary for :issue:`275`
+************************
+
+- Keep the list in alphabetical order.
+- In each row, enter:
+
+  **Name**
+     A short name for the module, function, or collection of such.
+  **m_data**
+     Link to one code or data file on the ``ssp_dev`` branch of ``message_data``, if any.
+     If there are multiple files, choose one.
+  **m_s_country**
+     Link to one code or data file on the ``SSP_Dev_2023`` branch of ``message_single_country``, if any.
+     If there are multiple files, choose one.
+     If the file is present in both message_data and message_single_country, these links should correspond in order to support diff of the two versions.
+  **m-ix-models**
+     Link to one code or data file on the ``main`` branch of ``message-ix-models``, for instance if the item has already been migrated as a dependency of other code.
+     If this migration has not happened yet, put "None".
+  **Pick**
+     Either "m_data", "m_single_country", or "m-ix-models", indicating which version of the code/data files will be preferred.
+  **PR/issue**
+     Link to, *at minimum*, a message-ix-models pull request that adds or updates the item, or an issue gathering more info than appears in the table.
+     Use the usual GitHub features to:
+
+     - Track the assignees, review assignments, status, checklist items, etc. associated with the PR.
+     - Cross-reference additional PRs that remove the corresponding files or code from message_data and/or message_single_country.
+
+.. list-table::
+   :header-rows: 1
+
+   * - Name
+     - m_data
+     - m_s_country
+     - m_ix_models
+     - Pick
+     - PR/issue
+
+   * - ``res_marg``
+     - :md-to-migrate:`link <message_data/scenario_generation/reserve_margin/res_marg.py>`
+     - :msc-to-migrate:`link <SSP_Dev_2023/models/modules/res_marg.py>`
+     - None
+     - TODO
+     - TODO
+
+.. Here are some further notes about this item.
+   Such notes **may** be kept here, but **must** be moved to an issue/PR as soon as one is opened, and deleted here.