build(buildscript):: add proxy example for windows

[Imitater967]

I believe this will help people setup proxy easier

[Imitater967]

as i know, the github in my country have a ultra slow downloading speed. that's why we need a proxy. the java/gradle don't accept the global proxy, until you adding -Dhttp.proxy.

in my country, we need proxy even for Android Studio, Spring boot, and any gradle project.

Trust me , proxy is very useful for some continent

[jdrueckert]

Trust me , proxy is very useful for some continent

In that case, this should be a country-specific note in the troubleshooting section of our docs, but not integrated in the scripts by default.

[soloturn]

a proxy is a standard configuration and should not go into gradlew, this is updated by gradlew update and wiped out. proxy can and should be set into the users or system environment, as HTTP_PROXY and HTTPS_PROXY. if this does not work, set GRADLE_OPTS and JAVA_OPTS into the users environment. if this is still not enough, please use something like direnv: https://direnv.net/ which exists for windows as well. if you feel this should go somewhere into the documentation, please change one of the doc files and reopen.