[book] Improve PostgreSQL configuration section
* Do not advice for specific PostgreSQL version (point to meta-packages if
available in Linux distros);
* First mention packages from Linux distros, put the link to official postgres
documentation at the end;
Closes #2725302.
The 'download' views
====================
.. automodule:: cubicweb.web.views.idownloadable
Components
----------
.. autoclass:: cubicweb.web.views.idownloadable.DownloadBox
Download views
--------------
.. autoclass:: cubicweb.web.views.idownloadable.DownloadView
.. autoclass:: cubicweb.web.views.idownloadable.DownloadLinkView
.. autoclass:: cubicweb.web.views.idownloadable.IDownloadablePrimaryView
.. autoclass:: cubicweb.web.views.idownloadable.IDownloadableLineView
Embedded views
--------------
.. autoclass:: cubicweb.web.views.idownloadable.ImageView
.. autoclass:: cubicweb.web.views.idownloadable.EHTMLView