Add build script and .gitignore to manage distribution files

.gitignore

@@ -0,0 +1 @@
+dist/

build.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+OUT_DIR="${ROOT_DIR}/dist"
+OUT_FILE="${OUT_DIR}/anti-bs-extension.zip"
+
+mkdir -p "${OUT_DIR}"
+
+(
+  cd "${ROOT_DIR}"
+  zip -r "${OUT_FILE}" \
+    manifest.json \
+    content.js \
+    popup.html \
+    popup.js \
+    popup.css \
+    icons \
+    README.md
+)
+
+echo "Built: ${OUT_FILE}"