update readme and add installation instructions

README.md

@@ -2,5 +2,20 @@
 
 Shaders for Avidemux with OpenGL support
 
-```unfish_gopro_8-7_wide_hypersmooth-off.glsl```  
-Fisheye removal for GoPro, 8:7 aspect ratio, wide FOV, HyperSmooth off
+## gopro_8:7 - Fisheye removal for GoPro 11+, 8:7 ratio
+- unfish_gopro_8:7.glsl  
+Shader for fisheye removal
+
+- preset_gopro_8:7_1080.py  
+Preset for mp4, 1656x1080, constant bitrate
+
+- compute_gopro_8:7.py  
+Script to compute output FOV and frame widening
+
+### Installation for BSD/GNU-Linux systems:
+- Copy the preset to ~/.avidemux6/custom/
+- Copy the shader to /opt/rk/avidemux/ (or edit the preset to set the path)  
+
+_For commercial OS's, figure out the paths yourself :)_
+### Usage:
+Load and edit video(s), select "Custom/preset_gopro_8:7_1080" in the menu and save the video.