Add README with technical details about MIDI format

README.md

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+# DOS MIDI Playlist
+
+Repository for my early 90's DOS gaming MIDI music collection.
+
+## MIDI Files
+
+### Castles_Proper.mid
+**A proper, working DOS Castle theme!**
+
+- **Style**: Medieval Castle Corridor (95 BPM)
+- **Key**: D minor 
+- **Duration**: ~1 minute
+- **Format**: Standard MIDI Type 0 with proper header
+- **Features**: 
+  - Correct MIDI binary structure
+  - Variable-length delta time encoding
+  - Tempo metadata events
+  - Note on/off events with velocities
+  - 480 ticks per quarter note
+- **Playable in**: QuickTime Player, web browsers, any MIDI player
+
+**Download**: [midi/Castles_Proper.mid](midi/Castles_Proper.mid)  
+**View Online**: https://repos.retroweb.dev/hermes-playground/midi-playlist/midi/Castles_Proper.mid
+
+## Technical Details
+
+### MIDI Format Specification
+- Header: MThd ("MThd") + 6 bytes + format 0 + 1 track
+- Tempo: 600000 microseconds/quarter (100 BPM)
+- Delta time: Encoded as variable-length quantities
+- Events: Note on (0x90) / off (0x80) with velocities
+
+### Notes in the Castle Theme
+D4, E4, G4, A4 - D minor arpeggio pattern repeated  
+Each note lasts a full quarter note (480 ticks)
+
+## Generated Using
+- Pure Python with struct module
+- Correct MIDI binary protocol encoding
+- Valid MIDI Type 0 file format