Add shell script showing how change TTY colors (#920)

## What are the changes about?

What was discussed in !912 before I accidentally caused it to auto merge (still not sure how that happened). I assume this is what was meant when asking for it to be in the startup script commented out.

## What existing issue does this resolve?

N/A

## Pre-requisites

- [x] I have tested & confirmed the changes work locally

Reviewed-on: https://codeberg.org/fairyglade/ly/pulls/920
Reviewed-by: AnErrupTion <anerruption@disroot.org>
Co-authored-by: hynak <hynak@noreply.codeberg.org>
Co-committed-by: hynak <hynak@noreply.codeberg.org>

build.zig

@@ -198,6 +198,8 @@ fn install_ly(allocator: std.mem.Allocator, patch_map: PatchMap, install_config:
         const patched_setup = try patchFile(allocator, "res/setup.sh", patch_map);
         try installText(patched_setup, config_dir, ly_config_directory, "setup.sh", .{ .mode = 0o755 });
 
+        try installFile("res/startup.sh", config_dir, ly_config_directory, "startup.sh", .{ .override_mode = 0o755 });
+
         try installFile("res/example.dur", config_dir, ly_config_directory, "example.dur", .{ .override_mode = 0o755 });
     }