Fix link in Electrum's doc
Originally created by @BitingBird on #8995 (Redmine)
https://tails.boum.org/doc/anonymous_internet/electrum says “the documentation on the Electrum website.” but the link is https://electrum.org/ when it should be https://electrum.orain.org/wiki/Main_Page (and probably renamed to “Electrum’s documentation”, because it’s not on their website anymore).