added some more documentation of Gridfunctions

4 jobs for issue/cleanup_gridfunctions in 21 minutes and 7 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #6941
debian:10 clang-6-libcpp-17

00:21:06

passed #6940
debian:10 gcc-8-17

00:16:53

passed #6942
debian:9 gcc-6-14

00:14:09

passed #6943
ubuntu:18.04 clang-6-17

00:19:46