[7.0] Update & Simplify install instructions (#2167)

* [7.0] Update install instructions

Now that we require PHP 7.1 and have greatly improved performance of backend placing hinst on performance tuning does not need to take space here anymore.

Besides that:
- updated to use dev, with symfony 3 builtin server is only available in dev by default
- update to use `/admin` url for backend
- somewhat simplified the text a bit

Open question:
- Do we need to run the assetic:dump command? As it's already ran by composer create-project which is what has been done when this is shown, ok if I remove?

* Update ScriptHandler.php

* Update ScriptHandler.php

* Update ScriptHandler.php

eZ/Bundle/EzPublishCoreBundle/Composer/ScriptHandler.php

@@ -119,24 +119,18 @@ public static function installWelcomeText(Event $event)
 <fg=cyan>Welcome to eZ Platform!</fg=cyan>
 
 <options=bold>Quick Install:</>
-(Assuming the CLI user you execute commands with below is same that extracted/installed the software)
-<comment>    $  export SYMFONY_ENV="prod"</comment>
+<comment>    $  export SYMFONY_ENV="dev"</comment>
 <comment>    $  php ${consoleDir}/console ezplatform:install <type></comment>
-<comment>    $  php ${consoleDir}/console assetic:dump</comment>
 <comment>    $  php ${consoleDir}/console server:run</comment>
 
 Note:
-- "ezplatform:install" has different installer <type>s depending on your install, see <fg=green>INSTALL.md</> or <fg=green>README.md</> for which one to use.
-- For development use you can enable full debugging by setting SYMFONY_ENV to "dev".
-- Last command will give you url to frontend of installation, add "/ez" to reach backend.
+- "ezplatform:install" has different installer <type>s depending on your install, run command with <comment>--help</comment> to see your options.
+- Instructions above assume the CLI user you execute these commands with is the same one that extracted/installed the software,
+  otherwise see install instructions for directory permissions.
+- The last command will give you the url to the frontend of the installation, add "/admin" to reach backend.
 
-Performance tips:
-- Use PHP 7.0 (or better yet PHP 7.1), and make sure opcache is enabled.
-- Dump autoload class map, even in development: <fg=green>composer dump-autoload --optimize</>
-- Follow full install instructions below to setup nginx (or Apache).
-- Further reading: https://doc.ezplatform.com/en/latest/guide/performance/
 
-For full install instructions, including setting up directory permissions, see install instructions in <fg=green>INSTALL.md</>
+For full install instructions, including setting up full web server & directory permissions, see install instructions in <fg=green>INSTALL.md</>
 or <fg=green>README.md</>.
 
 EOT