[FIX][IMP] doc: document manifest features (#22474)

Some manifest features, such as external_dependencies, hooks, etc. were
not previously documented, this commit documents these features.

Closes #22471

doc/reference/module.rst

@@ -1,5 +1,3 @@
-:banner: banners/module.jpg
-
 =======
 Modules
 =======
@@ -84,6 +82,49 @@ Available manifest fields are:
     to ``auto_install``. When both ``sale`` and ``crm`` are installed, it
     automatically adds CRM campaigns tracking to sale orders without either
     ``sale`` or ``crm`` being aware of one another
+``external_dependencies`` (``dict(key=list(str))``)
+    A dictionary containing python and/or binary dependencies.
+
+    For python dependencies, the ``python`` key must be defined for this
+    dictionary and a list of python modules to be imported should be assigned
+    to it.
+
+    For binary dependencies, the ``bin`` key must be defined for this
+    dictionary and a list of binary executable names should be assigned to it.
+
+    The module won't be installed if either the python module is not installed
+    in the host machine or the binary executable is not found within the
+    host machine's PATH environment variable.
+``application`` (``bool``, default: ``False``)
+    Whether the module should be considered as a fully-fledged application
+    (``True``) or is just a technical module (``False``) that provides some
+    extra functionality to an existing application module.
+``css`` (``list(str)``)
+    Specify css files with custom rules to be imported, these files should be
+    located in ``static/src/css`` inside the module.
+``images`` (``list(str)``)
+    Specify image files to be used by the module.
+``installable`` (``bool`` default: ``False``)
+    Whether a user should be able to install the module from the Web UI or not.
+``maintainer`` (``str``)
+    Person or entity in charge of the maintenance of this module, by default
+    it is assumed that the author is the maintainer.
+``{pre_init, post_init, uninstall}_hook`` (``str``)
+    Hooks for module installation/uninstallation, their value should be a
+    string representing the name of a function defined inside the module's
+    ``__init__.py``.
+
+    ``pre_init_hook`` takes a cursor as its only argument, this function is
+    executed prior to the module's installation.
+
+    ``post_init_hook`` takes a cursor and a registry as its arguments, this
+    function is executed right after the module's installation.
+
+    ``uninstall_hook`` takes a cursor and a registry as its arguments, this
+    function is executed after the module's uninstallation.
+
+    These hooks should only be used when setup/cleanup required for this module
+    is either extremely difficult or impossible through the api.
 
 .. _semantic versioning: http://semver.org
 .. _existing categories: