architecture: new doc with python module overview

docs/architecture.rst

+.. _architecture:
+
+Architecture
+============
+
+
+Python modules
+--------------
+
+.. _py-deps-swh:
+.. figure:: images/py-deps-swh.svg
+   :width: 1024px
+   :align: center
+
+   Dependencies among top-level Python modules (click to zoom).
+
+Here is brief overview of the most relevant Python modules in the Software
+Heritage Python stack (each module name is linked to its API documentation).
+
+:mod:`swh.archiver`
+    orchestrator in charge of guaranteeing that object storage content is
+    pristine and available in a sufficient amount of copies
+
+:mod:`swh.core`
+     low-level utilities and helpers used by almost all other modules in the
+     stack
+
+:mod:`swh.docs`
+     developer documentation (used to generate the docs you are reading)
+
+:mod:`swh.indexer`
+     tools and workers used to crawl the content of the archive and extract
+     derived information from any artifact stored in it
+
+:mod:`swh.journal`
+     persistent logger of changes to the archive, with publish-subscribe
+     support
+
+:mod:`swh.lister`
+     collection of listers for all sorts of source code hosting and
+     distribution places (forges, distributions, package managers, etc.)
+
+:mod:`swh.loader.core`
+     low-level loading utilities and helpers used by all other loaders
+
+:mod:`swh.loader.debian`
+     loader for `Debian <https://www.debian.org/>`_ source packages
+
+:mod:`swh.loader.dir`
+     loader for source directories (e.g., expanded tarballs)
+
+:mod:`swh.loader.git`
+     loader for `Git <https://git-scm.com/>`_ repositories
+
+:mod:`swh.loader.mercurial`
+     loader for `Mercurial <https://www.mercurial-scm.org/>`_ repositories
+
+:mod:`swh.loader.svn`
+     loader for `Subversion <https://subversion.apache.org/>`_ repositories
+
+:mod:`swh.loader.tar`
+     loader for source tarballs
+
+:mod:`swh.model`
+     implementation of the :ref:`data-model` to archive source code artifacts
+
+:mod:`swh.objstorage`
+     content-addressable object storage
+
+:mod:`swh.scheduler`
+     task manager for asynchronous/delayed tasks, used for recurrent (e.g.,
+     listing a forge, loading new stuff from a Git repository) and one-off
+     activities (e.g., loading a specific version of a source package)
+
+:mod:`swh.storage`
+     abstraction layer over the archive, allowing to access all stored source
+     code artifacts as well as their metadata
+
+:mod:`swh.vault`
+     implementation of the vault service, allowing to retrieve parts of the
+     archive as self-contained bundles (e.g., individual releases, entire
+     repository snapshots, etc.)
+
+:mod:`swh.web`
+     Web client to browse the archive, for both interactive (HTML UI) and
+     mechanized (REST API) use

docs/index.rst

@@ -6,6 +6,11 @@ Software Heritage - Development Documentation
    :caption: Contents:
 
 
+Overview
+--------
+
+* :ref:`architecture`
+
 
 Indices and tables
 ==================