Document config options

Closes #216

Author: RaphiMC

README.md

@@ -109,6 +109,19 @@ Known incompatibilities:
 
 If you encounter any issues, please report them on the [Issue Tracker](https://github.com/RaphiMC/ImmediatelyFast/issues).
 
+## Config
+ImmediatelyFast has a config file which can be found in the `config` folder of your Minecraft instance. Most options should be left at their default values, but some may be tweaked to improve performance or compatibility.  
+* `font_atlas_resizing`: Increases the sizes of the font atlas textures. This improves performance with high resolution or custom server fonts.
+* `map_atlas_generation`: Puts the map textures into a single texture instead of multiple textures. This improves performance when many maps are on screen.
+* `hud_batching`: Improves the performance of the HUD rendering by submitting less draw calls. If you experience issues with HUD elements, try disabling this optimization.
+* `fast_text_lookup`: Caches some data between rendering text characters. This slightly improves performance when rendering a lot of text.
+* `fast_buffer_upload`: Uploads data to the GPU in a more efficient way. This improves performance in general.
+* `experimental_disable_error_checking`: Disables OpenGL error checking. This may improve performance on certain systems, but can cause hard to debug issues if enabled.
+* `experimental_disable_resource_pack_conflict_handling`: Controls if ImmediatelyFast should scan resource packs for incompatible core shader modifications in oder to disable some conflicting optimizations. This can be disabled to force optimizations even if they may cause graphical issues with certain resource packs.
+* `experimental_sign_text_buffering`: Buffers text on signs instead of re-rendering it every frame. May cause issues with high resolution or custom fonts.
+* `experimental_screen_batching`: Improves the performance of some in-game screens rendering by submitting less draw calls.
+* `experimental_universal_hud_batching`: More aggressive HUD batching. More likely to cause issues with HUD elements.
+
 ## Developer API
 You can read the API docs [here](docs/API_DOCS.md).