Custom built version looks for files in the build directory

[arminfuerst]

To distribute Gittyup to my local clients, I'd like to build it myself and package it (Linux/Debian).
Building according to https://github.com/Murmele/Gittyup/blob/master/README.md seems to work. I checkout the version (currently commit 6bf49f0).
From the root of the repo, I use following commands:

git submodule update
cd dep/openssl/openssl
./config -fPIC
make
cd ../../..
mkdir -p build/release
cd build/release
cmake -G Ninja -DCMAKE_BUILD_TYPE=Release ../..
ninja

This results in a version in build/release I can start.
I have following issues with this version:

• "Help" -> "About Gittyup" displays empty text boxes for "Changelog", "Acknowledgments" and "Privacy". The console prints that the files are looked for in an absolute directory dependent from the build directory: QTextBrowser: No document for file:///<GIT ROOT FOR GITTYUP>/conf/changelog.html
• The lua-files for the themes are also used from the git-repo: PANIC: unprotected error in call to Lua API (cannot open <GIT ROOT FOR GITTYUP>/conf/System.lua: No such file or directory)

I assume, I need to provide an additional parameter when configuring and I just can't figure out. Or there is a different solution. Anyway it would be good to include these details in README.md

[alerque]

Duplicate with #769.