Added Installation guide for Gitlab Pages

[kolibril13]

As this might be useful for other people as well.

[kolibril13]

Closes #583

[mgeier]

Thanks for this PR!

There are a lot of unrelated changes, do you know why? Do you know how to avoid them?

[mgeier]

Can you please rebase on master in order to fix the build error?

[kolibril13]

git rebase master
Current branch added-installation is up to date.

this is what I get.

[mgeier]

You should first git pull the latest master branch.

[kolibril13]

then I get this:

git pull
Already up to date.

[mgeier]

That's strange.

The branch of this PR is currently at 7334341, and its base (the parent of your first commit) is 4fb5586 (which at some point was the master branch of this repo).
In the meantime, the master branch has progressed to d75cf07.

What is the hash of your master branch?

Probably you have to pull from a different remote?

[kolibril13]

closed for #597