Fix procedure of how to create update site

[frauzufall]

Problem:
The "Add my site" button currently asks for the wiki password in order to initialize the update site password. This functionality is currently broken (it does not accept the correct password).

How it should work:
After clicking the "Add my site" button https://imagej.net/Special:ChangeUploadPassword should be opened in order to initialize the password.

Also the wiki page needs to be updated afterwards.