I found out that the srfi's already used live under /user/guile/3.0/srfi/. This is also in the load-path variable. Now I go into /user/guile/3.0/srfi/ and 'git clone github-link-to-srfi-25' but I can not load the code via
(use-module
(srfi srfi-25))
in geiser. I noticed that the other srfi's living there don't consist of git projects and also sometimes are 100 % html code so I am really confused right now on how to use code in the srfi. Do I have to define the module myself?