commit the new README on release

Author: mmomtchev

package.json

@@ -11,7 +11,7 @@
     "lint": "clang-format -i src/*.cc src/*.h && eslint lib/*.js test/*.js bench/*.js scripts/*.js",
     "bench": "node bench/bench.js",
     "doc": "documentation readme --section=API --config=documentation.yml src/*.cc",
-    "preversion": "npm run lint && npm run test && npm run doc",
+    "preversion": "npm run lint && npm run test && npm run doc && git add README.md",
     "version": "git add package.json",
     "postversion": "git push && git push --tags && node ./scripts/publish-packages.js",
     "gcov": "mkdir -p coverage && cd coverage && gcov -o ../build/Debug/obj.target/exprtk.js/src ../src/*",