Update user-groups.md
Update user-groups.md

updated Rust Bangalore URL with the Meetup page URL https://www.meetup.com/rustox/
AndrewBrinker/rust-www,AndrewBrinker/rust-www,AndrewBrinker/rust-www,AndrewBrinker/rust-www,AndrewBrinker/rust-www,AndrewBrinker/rust-www