Make it easier to solve nginx build stuck

DOCUMENTATION/content/documentation/index.md

@@ -1680,3 +1680,7 @@ This error sometimes happens because your Laravel application isn't running on t
   2. Change the `DB_HOST` variable on env with the IP that you received from previous step.
 * Option B
    1. Change the `DB_HOST` value to the same name as the MySQL docker container. The Laradock docker-compose file currently has this as `mysql`
+
+## I get stuck when building ngxinx on `fetch http://mirrors.aliyun.com/alpine/v3.5/main/x86_64/APKINDEX.tar.gz`
+
+As stated on [#749](https://github.com/laradock/laradock/issues/749#issuecomment-293296687), removing the line `RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/' /etc/apk/repositories` from `nginx/Dockerfile` solves the problem.