minor #8721 Overhaul Deployment + a few other tweaks (weaverryan)

This PR was squashed before being merged into the 4.0 branch (closes #8721).

Discussion
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Overhaul Deployment + a few other tweaks

This removes all of the PAAS articles. I *really* like mentioning great PaaS, but it doesn't make sense for us to maintain the articles (and in practice, we don't maintain them).

So, I've removed all of the articles. Ping @dzuelke, @Crell & @ostark. I just want you guys to be aware of this :).

This updates `deployment.rst` to mention environment variables. But my description is SUPER weak (https://github.com/symfony/symfony-docs/pull/8721/files#diff-7691c197e7985b35df39ae74d6d58b8dR128)! My impression is that (outside a PaaS), setting environment variables is a pain, and varies widely. I want to give a better recommendation that I am right now.

Commits
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3e463f6 updating link to be version independent
5b6ef2a linking directly and marking articles as orphans
9a1695d linking to missing article
bbffb1a Removing all PAAS deployment articles
b563ab2 using different example

Author: weaverryan

components/dependency_injection/_imports-parameters-note.rst.inc

@@ -10,7 +10,7 @@
 
             # app/config/config.yml
             imports:
-                - { resource: '%kernel.project_dir%/app/parameters.yml' }
+                - { resource: '%kernel.project_dir%/somefile.yml' }
 
         .. code-block:: xml
 
@@ -22,11 +22,11 @@
                     http://symfony.com/schema/dic/services/services-1.0.xsd">
 
                 <imports>
-                    <import resource="%kernel.project_dir%/app/parameters.yml" />
+                    <import resource="%kernel.project_dir%/somefile.yml" />
                 </imports>
             </container>
 
         .. code-block:: php
 
             // app/config/config.php
-            $loader->import('%kernel.project_dir%/app/parameters.yml');
+            $loader->import('%kernel.project_dir%/somefile.yml');

deployment.rst

@@ -63,14 +63,13 @@ manually taking other steps (see `Common Post-Deployment Tasks`_).
 Using Platforms as a Service
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-The specific deployment steps vary greatly from one service provider to another,
-so check out the dedicated article for the service of your choose:
+Using a Platform as a Service (PaaS) can be a great way to deploy your Symfony app
+quickly and easily. There are many PaaS - below are a few that work well with Symfony:
 
-.. toctree::
-    :maxdepth: 1
-    :glob:
-
-    deployment/*
+* `Heroku`_
+* `Platform.sh`_
+* `Azure`_
+* `fortrabbit`_
 
 Using Build Scripts and other Tools
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -123,18 +122,16 @@ Check if your server meets the requirements by running:
 
 .. _b-configure-your-app-config-parameters-yml-file:
 
-B) Configure your Parameters File
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+B) Configure your Environment Variables
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Most Symfony applications define configuration parameters in a file called
-``app/config/parameters.yml``. This file should *not* be deployed, because
-Symfony generates it automatically using the ``app/config/parameters.yml.dist``
-file as a template (that's why ``parameters.yml.dist`` must be committed and
-deployed).
+Most Symfony applications read their configuration from environment variables.
+While developing locally, you'll usually store these in a ``.env`` file. But on
+production, instead of creating this file, you should set *real* environment variables.
 
-If your application uses environment variables instead of these parameters, you
-must define those env vars in your production server using the tools provided by
-your hosting service.
+How you set environment variables, depends on your setup: they can be set at the
+command line, in your Nginx configuration, or via other methods provided by your
+hosting service.
 
 C) Install/Update your Vendors
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -237,6 +234,14 @@ kernel and return your project's root directory::
         }
     }
 
+Learn More
+----------
+
+.. toctree::
+    :maxdepth: 1
+
+    deployment/proxies
+
 .. _`Capifony`: https://github.com/everzet/capifony
 .. _`Capistrano`: http://capistranorb.com/
 .. _`sf2debpkg`: https://github.com/liip/sf2debpkg
@@ -249,3 +254,7 @@ kernel and return your project's root directory::
 .. _`Symfony plugin`: https://github.com/capistrano/symfony/
 .. _`Deployer`: http://deployer.org/
 .. _`Git Tagging`: https://git-scm.com/book/en/v2/Git-Basics-Tagging
+.. _`Heroku`: https://devcenter.heroku.com/articles/getting-started-with-symfony
+.. _`platform.sh`: https://docs.platform.sh/frameworks/symfony.html
+.. _`Azure`: https://azure.microsoft.com/en-us/develop/php/
+.. _`fortrabbit`: https://help.fortrabbit.com/install-symfony