Write some amount of documentation

docs/grid.md

@@ -0,0 +1,54 @@
+# The Sequencer Grid
+
+The sequencer grid is the heart of Cagire. Each cell represents a step that can contain a Forth script to generate sound.
+
+## Structure
+
+- **Steps**: Up to 128 per pattern, displayed 32 at a time
+- **Patterns**: Up to 32 per bank
+- **Banks**: Up to 32 per project
+
+## Navigation
+
+Use arrow keys to move between steps. The grid wraps around at pattern boundaries.
+
+## Selection
+
+Hold `Shift` while pressing arrow keys to select multiple steps. Press `Esc` to clear the selection.
+
+## Editing Steps
+
+- `Enter` - Open the script editor
+- `t` - Toggle step active/inactive
+- `r` - Rename a step
+- `Del` - Delete selected steps
+
+## Copy & Paste
+
+- `Ctrl+C` - Copy selected steps
+- `Ctrl+V` - Paste as copies
+- `Ctrl+B` - Paste as linked steps
+- `Ctrl+D` - Duplicate selection
+- `Ctrl+H` - Harden links (convert to copies)
+
+Linked steps share the same script as their source. When you edit the source, all linked steps update automatically.
+
+## Pattern Controls
+
+- `<` / `>` - Decrease/increase pattern length
+- `[` / `]` - Decrease/increase pattern speed
+- `L` - Set length directly
+- `S` - Set speed directly
+
+## Playback
+
+- `Space` - Toggle play/stop
+- `+` / `-` - Adjust tempo
+- `T` - Set tempo directly
+- `Ctrl+R` - Run current step once (preview)
+
+## Visual Indicators
+
+- **Highlighted cell** - Currently playing step
+- **Colored backgrounds** - Linked steps share colors by source
+- **Arrow prefix** (→05) - Step is linked to step 05