Update lang readme to match reality

[xrmx]

It looks like i18n updates are done manually editing files there. http://translate.jitsi.org is not there anymore.

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[damencho]

We are working to put back translate.jitsi.org back in place ... Just more priority tasks moves that back in the list. Will see how it goes with the weekly plan and can merge of we cannot finish the move in the following few weeks.

[saghul]

@damencho How is this week looking? We could land this and revert it once we have the plan inplace.

[MagicFab]

So yeah, my pull request with useful information was rejected in favor of keeping a vague mention of "manually editing the files". Just adding this here for reference.