user: Bootstrap loaders high-level documentation

Add landing page of loaders high-level documentation displaying
available ones in a table with the following column:

  - logo and name of the loader linking to its specific documentation

  - related links: source code, developer doc, development activity

  - current status: production, staging or development

  - link to related grant if any

Create one rst file per loader to further document.

Related to T3117

docs/_static/custom.css

@@ -378,4 +378,18 @@ a {
     local('Alegreya Sans-Blackitalic'),
     url(fonts/alegreya-sans-latin-900italic.woff2) format('woff2'),
     url(fonts/alegreya-sans-latin-900italic.woff) format('woff'); /* Modern Browsers */
-}
\ No newline at end of file
+}
+
+table.swh-logos-table td,
+table.swh-logos-table th {
+  text-align: center;
+}
+
+table.swh-logos-table img {
+  margin-bottom: 5px;
+}
+
+table.swh-logos-table ul {
+  text-align: left;
+  margin-bottom: auto;
+}

swh/docs/sphinx/conf.py

@@ -120,6 +120,7 @@ html_logo = "_static/software-heritage-logo-title-motto-vertical-white.png"
 html_static_path = ["_static"]
 
 html_js_files = ["custom.js"]
+html_css_files = ["custom.css"]
 
 # make logo actually appear, avoiding gotcha due to alabaster default conf.
 # https://github.com/bitprophet/alabaster/issues/97#issuecomment-303722935

user/index.rst

 .. _swh-docs:
 
-.. Software Heritage documentation master file, created by
-   sphinx-quickstart on Thu Jun 17 11:23:12 2021.
-   You can adapt this file completely to your liking, but it should at least
-   contain the root `toctree` directive.
-
 Software Heritage User documentation
 ====================================
 
 Getting started
 ---------------
 * :ref:`faq`
-
-Tutorials
----------
-
-...
+* :ref:`loaders`
 
 
 Indices and tables
@@ -27,9 +18,10 @@ Indices and tables
 
 
 .. toctree::
-   :maxdepth: 2
-   :caption: Contents:
-   :titlesonly:
-   :hidden:
+  :maxdepth: 2
+  :caption: Contents:
+  :titlesonly:
+  :hidden:
 
-   faq/index
+  faq/index
+  loaders/index

user/loaders/archive.rst

+.. _archive_loader:
+
+Archive loader
+==============
+
+.. todo::
+   This page is a work in progress.

user/loaders/bazaar.rst

+.. _bzr_loader:
+
+Bazaar loader
+=============
+
+.. todo::
+   This page is a work in progress.

user/loaders/cran.rst

+.. _cran_loader:
+
+CRAN loader
+===========
+
+.. todo::
+   This page is a work in progress.

user/loaders/crates.rst

+.. _crates_loader:
+
+Crates loader
+=============
+
+.. todo::
+   This page is a work in progress.

user/loaders/cvs.rst

+.. _cvs_loader:
+
+CVS loader
+==========
+
+.. todo::
+   This page is a work in progress.

user/loaders/debian.rst

+.. _debian_loader:
+
+Debian loader
+=============
+
+.. todo::
+   This page is a work in progress.

user/loaders/deposit.rst

+.. _deposit_loader:
+
+Deposit loader
+==============
+
+.. todo::
+   This page is a work in progress.

user/loaders/git.rst

+.. _git_loader:
+
+Git loader
+==========
+
+.. todo::
+   This page is a work in progress.

user/loaders/maven.rst

+.. _maven_loader:
+
+Maven loader
+============
+
+.. todo::
+   This page is a work in progress.

user/loaders/mercurial.rst

+.. _mercurial_loader:
+
+Mercurial loader
+================
+
+.. todo::
+   This page is a work in progress.

user/loaders/nixguix.rst

+.. _nixguix_loader:
+
+NixGuix loader
+==============
+
+.. todo::
+   This page is a work in progress.

user/loaders/npm.rst

+.. _npm_loader:
+
+NPM loader
+==============
+
+.. todo::
+   This page is a work in progress.

user/loaders/opam.rst

+.. _opam_loader:
+
+Opam loader
+===========
+
+.. todo::
+   This page is a work in progress.

user/loaders/pypi.rst

+.. _pypi_loader:
+
+PyPI loader
+===========
+
+.. todo::
+   This page is a work in progress.

user/loaders/subversion.rst

+.. _subversion_loader:
+
+Subversion loader
+=================
+
+.. todo::
+   This page is a work in progress.