New page for managing text files in mods

Co-authored-by: Kade <26305836+Kade-github@users.noreply.github.com>

Author: spark-the-dragon

assets/content/cookbook/Advanced/9.UsingTextFiles.md

@@ -0,0 +1,61 @@
+[tags]: / "advanced,txt,haxe"
+
+# Text Files
+
+While not used much by Friday Night Funkin' (in exception to `introText.txt`), the ability to read and save to text files may be useful for some mods. 
+
+## Reading a .txt file
+
+To read a text file, you will not need any imports, by default `funkin.Paths` is imported into scripts, which is what we need to access text files.
+
+The text file must exist to be read and have content in it to be read by the game. The text file will be read from the `data` folder of your mod.
+
+Below is an example of how to read a text file.
+
+```haxe
+import funkin.play.song.Song;
+
+class Tutorial extends Song {
+    var data:String = ''; // This variable will contain the text when we read the text file.
+    public function new() 
+    {
+        super("bopeebo"); // This is the song name, it must be lowercase here.
+    }
+    
+    function onSongLoaded(event:ScriptEvent):Void {
+        super.onSongLoaded(event);
+        data = Assets.getText(Paths.txt("Player")); // Txt file, ALWAYS in "data" folder.
+        trace('text contents are ' + data); // Prints contents of text file in the console.
+    }
+}
+```
+
+## Saving to a .txt file
+
+Unlike reading a text file, some more things will need to be imported to correctly save a text file. More specifically you will need to import the following:
+"-`funkin.util.FileUtil`"
+
+This is needed to save text files. Like reading a text file, the text files MUST be in your `data` folder in your mod, and must already exist before attempting to save to it (the game will NOT create a text file if it does not already exist).
+
+Below is an example of how to save a text file.
+
+```haxe
+import funkin.play.song.Song;
+import funkin.util.FileUtil; // Required module to save text files
+
+class Tutorial extends Song {
+    public function new() 
+    {
+        super("bopeebo"); // This must be the song name just lowercased
+    }
+    
+    override public function onCreate():Void // This will be called upon the game starting
+    {
+        super.onCreate();
+        FileUtil.writeStringToPath(Assets.getPath(Paths.txt("Player")), 'extra large potato'); 
+        // Above will save to our mod's data folder to the text file named "Player.txt" and will write "extra large potato" in said text file
+    }
+}
+```
+
+> Author: [Spark the Dragon](https://github.com/spark-the-dragon)