chore: add a comment illustrate why we build packages sequentially

.esbuild/build.ts

@@ -56,6 +56,7 @@ const main = async () => {
   generateLangium();
   await mkdir('stats').catch(() => {});
   const packageNames = Object.keys(packageOptions) as (keyof typeof packageOptions)[];
+  // it should build `parser` before `mermaid` because it's a dependecy
   for (const pkg of packageNames) {
     await buildPackage(pkg).catch(handler);
   }