docs: usage block + full usage guide

Author: CoderDeltaLAN

docs/USAGE.md

@@ -0,0 +1,23 @@
+# Diff Risk Dashboard — Usage
+
+## Short wrappers
+- `drt <apv.json | raw-json>`: tabla a color (TTY)
+- `drb <apv.json | raw-json>`: barras (logs)
+- `drj <apv.json | raw-json>`: JSON (CI)
+- `drmd <apv.json | raw-json>`: Markdown (stdout)
+
+```bash
+drt examples/sample_apv.json
+drt '{"by_severity":{"CRITICAL":0,"HIGH":1,"MEDIUM":1,"LOW":1,"INFO":0}}'
+APV="/ruta/real/a/tu_apv.json"; drt "$APV"
+```
+
+Agregar al PATH (opcional):
+```bash
+mkdir -p ~/.local/bin && ln -sf "$PWD/bin/"* ~/.local/bin/ && hash -r
+```
+
+CLI crudo:
+```bash
+poetry run diff-risk <input> -f table|bar|json|md --no-exit-by-risk
+```