doc: add code completion section to README

README.md

@@ -76,6 +76,42 @@ The input window accepts multi-line prompts. Queued prompts are held until the c
 
 The mode line shows the active session ID and current state (`idle` or the running state name).
 
+## Code Completion
+
+`ellie-complete` provides ghost-text code completion via a copilot session on ollie-9p. Press `M-/` to request a completion at point; the result appears as gray italic ghost text.
+
+| Key | Action |
+|-----|--------|
+| `M-/` | Request completion at point (or for selected region) |
+| `TAB` / `RET` | Accept the suggestion |
+| Any other key | Dismiss |
+| `M-/` (while ghost visible) | Request a new completion (retries preserve region) |
+
+With an active region, the completion replaces the selected text. Without a region, it inserts after the current line.
+
+### Configuration
+
+| Variable | Env var | Description |
+|----------|---------|-------------|
+| `ellie-complete-backend` | `OLLIE_COMPLETE_BACKEND` | Backend for completion (required) |
+| `ellie-complete-model` | `OLLIE_COMPLETE_MODEL` | Model for completion (required) |
+| `ellie-complete-prefix-max` | — | Max chars of context before point (default: 4000) |
+| `ellie-complete-suffix-max` | — | Max chars of context after point (default: 1000) |
+
+Example:
+
+```elisp
+(setq ellie-complete-backend "ollama")
+(setq ellie-complete-model "qwen3:4b")
+```
+
+Or via environment / `~/.config/ollie/env`:
+
+```
+OLLIE_COMPLETE_BACKEND=ollama
+OLLIE_COMPLETE_MODEL=qwen3:4b
+```
+
 ## License
 
 GPLv3