Slim down the "How to help running Snowflake proxies" entry

On https://support.torproject.org/censorship/how-to-help-running-snowflake/ we have instructions for how to volunteer to be a snowflake, but they are incomplete and out of date compared to the instructions on https://snowflake.torproject.org/#extension

I have opened tpo/anti-censorship/pluggable-transports/snowflake-webext#87 (moved) for the snowflake.tpo page to add the two pieces of info that are currently only on the support entry ("enable webrtc" and "not on a VPN please"), and then when that is done we should remove all the instructions from the support entry.

Though that said, we could also just remove them from the support entry right now, and point to the snowflake.tpo page, and then we won't add a dependency step that doesn't really need to be a dependency. :)