Document environment variable we support

I propose an improvement for RelativeLink.sh. Only comments are changed.

If there is no progress in legacy/trac#5611 (moved) perhaps we can at least improve the script comments?

git commit message: RelativeLink.sh: Only comments changed. ## for comments, # for commented out commands. Documented TOR_TRANSPROXY, TOR_SOCKS_HOST and TOR_SOCKS_PORT.

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