Misleading Entry Point 'main.asm' and 'xor' line preventing compilation

[LaroldsJubilantJunkyard]

Two issues pointed out by @bpf on the gbdev/asm-rgbds channel.

1. The 'main.asm' file is not the actual entrypoint, but that might be confusing for a lot of people. the actual entry point is the src/main/GalacticArmada.asm file. Code snippets should be adjusted to reflect this.
2. Getting an error of syntax error, unexpected newline in the enemies.asm file. There's a naked xor statement (no registers specified)

The discord messages for reference:

• https://discord.com/channels/303217943234215948/790920525253836912/1233463299941732363
• https://discord.com/channels/303217943234215948/790920525253836912/1233463392937709578