add installation readme

Installation.md

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+- Open https://docs.opensupports.com/guides/installation
+  (keep it open in a separate tab so you can refer it during installation)
+
+- Login to the hostinger account (you should have a website created already)
+
+- In hostinger (or your hosting server),
+  update the php version to one that is supported by open supports (7.4 as of 2023 January)
+
+- Download the zip file from
+  http://www.opensupports.com/download/ which has the latest stable version of OpenSupports.
+- Unzip the package in a folder of your server, for example: yourwebsite.com/support
+
+- Go to yourwebsite.com/support (or the place where you extracted the file) and it
+  should take you to the installation wizard.
+
+Troubleshooting:
+
+- the installation wizard might not appear sometimes, follow this step to make it appear,
+
+  - check if php pdo plugin is enabled in the webserver (from your hosting server, access php settings)
+  - There will be an error in the backend with call to get_magic_quotes_gpc(),
+    Solution:
+    Open the file api/vendor/slim/slim/Slim/Http/Util.php
+    and find the line 60
+    $strip = is_null($overrideStripSlashes) ? get_magic_quotes_gpc() : $overrideStripSlashes;
+      and replace it with
+      $strip = $overrideStripSlashes;
+
+    reference:
+    https://stackoverflow.com/questions/61054418/php-7-4-deprecated-get-magic-quotes-gpc-function-alternative
+    https://github.com/opensupports/opensupports/issues/908
+
+    ***
+
+- Database creation step will fail sometimes, for this, do the following,
+  Create the database manually from tools provided by the hosting provider (or via phpmyadmin)
+  manually update the config.php with the following content with the new created sql db values
+
+   <?php
+       define('MYSQL_HOST', '127.0.0.1');
+       define('MYSQL_PORT', '3306');
+       define('MYSQL_USER', 'user');
+       define('MYSQL_PASSWORD', 'user');
+       define('MYSQL_DATABASE', 'dbname');
+   ?>
+
+  Now you might be facing the INIT_SETTINGS_DONE error which you can resolve and get to the next step by
+  removing the following line from config.php
+  define('MYSQL_HOST', '127.0.0.1');
+  Now in the installation wizard step for db connection, fill the hostname and other values such as username and
+  db name should match what was created in the config
+  And then fill the hostname in the My SQL config form in the installation wizard.
+
+  reference: https://github.com/opensupports/opensupports/issues/176