docs: align testing guide with CI

scripts/run_integration_tests.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+#
+# Runs the real-API integration tests for polyfill-rs.
+#
+# These tests hit the live Polymarket API and are `#[ignore]` by default.
+# You must provide credentials via environment variables or a local `.env` file.
+
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$ROOT_DIR"
+
+echo "Running ignored integration tests against the live Polymarket API..."
+
+if [[ -z "${POLYMARKET_PRIVATE_KEY:-}" ]]; then
+  if [[ -f .env ]] && grep -q '^POLYMARKET_PRIVATE_KEY=' .env; then
+    echo "Using POLYMARKET_PRIVATE_KEY from .env"
+  else
+    echo "ERROR: POLYMARKET_PRIVATE_KEY is not set (env or .env)."
+    echo "Set POLYMARKET_PRIVATE_KEY in your environment or add it to .env."
+    exit 1
+  fi
+fi
+
+set -x
+
+# Run serially to reduce the chance of hitting rate limits.
+cargo test --all-features --test integration_tests -- --ignored --nocapture --test-threads=1
+cargo test --all-features --test simple_auth_test -- --ignored --nocapture --test-threads=1
+cargo test --all-features --test order_posting_test -- --ignored --nocapture --test-threads=1