[docs] Add templates and examples of renos

With tips and clarifications.

Adapted from Kolla Ansible's patch. [1]

[1] https://review.opendev.org/c/openstack/kolla-ansible/+/759254

Change-Id: I07490bc3a7809415fe1734aee255143c205d9573

doc/source/contributor/release-notes.rst

@@ -4,6 +4,9 @@
 Release notes
 =============
 
+Introduction
+~~~~~~~~~~~~
+
 Kolla uses the following release notes sections:
 
 - ``features`` --- for new features or functionality; these should ideally
@@ -33,9 +36,15 @@ To add a release note, run the following command:
    tox -e venv -- reno new <summary-line-with-dashes>
 
 All release notes can be inspected by browsing ``releasenotes/notes``
-directory.
+directory. Further on this page we show reno templates, examples and how to
+make use of them.
 
-To generate release notes in HTML format in ``releasenotes/build``, run:
+.. note::
+
+  The term `release note` is often abbreviated to `reno` as it is the name of
+  the tool that is used to manage the release notes.
+
+To generate renos in HTML format in ``releasenotes/build``, run:
 
 .. code-block:: console
 
@@ -43,3 +52,121 @@ To generate release notes in HTML format in ``releasenotes/build``, run:
 
 Note this requires the release note to be tracked by ``git`` so you
 have to at least add it to the ``git``'s staging area.
+
+The release notes are linted in the CI system. To lint locally, run:
+
+.. code-block:: console
+
+   tox -e doc8
+
+The above lints all of documentation at once.
+
+Templates and examples
+~~~~~~~~~~~~~~~~~~~~~~
+
+All approved release notes end up being published on a dedicated site:
+
+   https://docs.openstack.org/releasenotes/kolla/
+
+When looking for examples, it is advised to consider browsing the page above
+for a similar type of change and then comparing with their source
+representation in ``releasenotes/notes``.
+
+The sections below give further guidelines. Please try to follow them but note
+they are not set in stone and sometimes a different wording might be more
+appropriate. In case of doubt, the core team will be happy to help.
+
+Features
+--------
+
+Template
+++++++++
+
+.. path releasenotes/templates/feature.yml
+.. code-block:: yaml
+
+   ---
+   features:
+     - |
+       Implements [some feature].
+       [Can be described using multiple sentences if necessary.]
+       [Limitations worth mentioning can be included as well.]
+       `Blueprint [blueprint id] <https://blueprints.launchpad.net/kolla/+spec/[blueprint id]>`__
+
+.. note::
+
+  The blueprint can be mentioned even if the change implements it only
+  partially. This can be emphasised by preceding the ``Blueprint`` word by
+  ``Partial``. See the example below.
+
+Example
++++++++
+
+Implementing blueprint with id `letsencrypt-https`, we use ``reno`` to generate
+the scaffolded file:
+
+.. code-block:: console
+
+   tox -e venv -- reno new --from-template releasenotes/templates/feature.yml blueprint-letsencrypt-https
+
+.. note::
+
+  Since we don't require blueprints for simple features, it is allowed to
+  make up a blueprint-id-friendly string (like in the example here) ad-hoc
+  for the proposed feature. Please then skip the ``blueprint-`` prefix to
+  avoid confusion.
+
+And then fill it out with the following content:
+
+.. code-block:: yaml
+
+   ---
+   features:
+     - |
+       Implements support for hassle-free integration with Let's Encrypt.
+       The support is limited to operators in the underworld.
+       For more details check the TLS docs of Kolla.
+       `Partial Blueprint letsencrypt-https <https://blueprints.launchpad.net/kolla/+spec/letsencrypt-https>`__
+
+.. note::
+
+  The example above shows how to introduce a limitation. The limitation may be
+  lifted in the same release cycle and it is OK to mention it nonetheless.
+  Release notes can be edited later as long as they have not been shipped in
+  an existing release or release candidate.
+
+Fixes
+-----
+
+Template
+++++++++
+
+.. path releasenotes/templates/fix.yml
+.. code-block:: yaml
+
+   ---
+   fixes:
+     - |
+       Fixes [some bug].
+       [Can be described using multiple sentences if necessary.]
+       [Possibly also giving the previous behaviour description.]
+       `LP#[bug number] <https://launchpad.net/bugs/[bug number]>`__
+
+Example
++++++++
+
+Fixing bug number `1889611`, we use ``reno`` to generate the scaffolded file:
+
+.. code-block:: console
+
+   tox -e venv -- reno new --from-template releasenotes/templates/fix.yml bug-1889611
+
+And then fill it out with the following content:
+
+.. code-block:: yaml
+
+   ---
+   fixes:
+     - |
+       Fixes ``deploy-containers`` action missing for the Masakari role.
+       `LP#1889611 <https://launchpad.net/bugs/1889611>`__

releasenotes/templates/feature.yml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Implements [some feature].
+    [Can be described using multiple sentences if necessary.]
+    [Limitations worth mentioning can be included as well.]
+    `Blueprint [blueprint id] <https://blueprints.launchpad.net/kolla/+spec/[blueprint id]>`__

releasenotes/templates/fix.yml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixes [some bug].
+    [Can be described using multiple sentences if necessary.]
+    [Possibly also giving the previous behaviour description.]
+    `LP#[bug number] <https://launchpad.net/bugs/[bug number]>`__