[ADD] guidelines: media files section in content guidelines

Author: jcs-odoo

contributing/documentation/content_guidelines.rst

@@ -160,6 +160,42 @@ A few tips to improve your screenshots:
    Resizing the window's width is the most important step to do as Odoo's responsive design
    automatically resizes all fields to match the window's width.
 
+.. _contributing/media-files:
+
+Media files
+-----------
+
+A **media filename** is written in **lower-case letters** and is composed of two parts:
+
+#. An **identifying name** relevant to the media's content. E.g., ``awesome-filename``.
+
+   .. important::
+      Use a **hyphen** ``-`` to separate the words in the media filename.
+
+#. The **file extension**, which is ``.png`` for most images.
+
+Each document has its own folder in which the media files are located. The folder's name must be the
+same as the document's filename.
+
+For example, the document :file:`doc_filename.rst` refers to two images that are placed in the
+folder ``doc_filename``.
+
+::
+
+  ├── section
+  │   └── doc_filename
+  │   │   └── something.png
+  │   │   └── awesome-filename.png
+  │   └── doc_filename.rst
+
+
+.. note::
+   Previously, image filenames would mostly be named with numbers (e.g., :file:`feature01.png`) and
+   placed in a single ``media`` folder. While it is advised not to name your *new* images in that
+   fashion, it is also essential **not to rename unchanged files**, as doing this would double the
+   weight of renamed image files on the repository. They will eventually all be replaced with new
+   content.
+
 .. _contributing/alt-tags:
 
 ALT tags