[Documentation] Move all wiki pages into the repo and make it pretty (#2494)

docs/04_For_Developers/05_Debug_mode.md

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+<h1 align="center">Warning!</h1>
+
+Enabling debug mode on a public server may result in malicious clients retrieving sensitive data about your server and possibly gaining access to it. Do not enable debug mode on a public server, unless you understand the implications of your doing!
+
+***
+
+Debug mode enables error reporting and prevents loading data from the cache (data is still written to the cache).
+To enable debug mode, create a file named 'DEBUG' in the root directory of RSS-Bridge (next to `index.php`). For further security, insert your IP address in the file. You can add multiple addresses, one per line.
+
+_Notice_:
+
+* An empty file enables debug mode for anyone!
+* The bridge whitelist still applies! (debug mode does **not** enable all bridges)
+
+RSS-Bridge will give you a visual feedback when debug mode is enabled:
+
+![twitter bridge](../images/debug_mode.png)
+
+While debug mode is active, RSS-Bridge will write additional data to your servers `error.log`.
+
+Debug mode is controlled by the static class `Debug`. It provides three core functions:
+
+`Debug::isEnabled()`: Returns `true` if debug mode is enabled.
+`Debug::isSecure()`: Returns `true` if your client is on the debug whitelist.
+`Debug::log($message)`: Adds a message to `error.log`. It takes one parameter, which can be anything. For example: `Debug::log('Hello World!');`
+
+**Notice**: `Debug::log($message)` calls `Debug::isEnabled()` internally. You don't have to do that manually.