I see - no worries 
There are two options:
Option 1: Install it from your Linux distribution’s repository
You can try to install from your Linux repository, e.g. for Debian:
apt-get install rtl-433
If this installs a reasonable recent version of rtl_433 - fine. If not, you need to let your Linux compile a fresh rtl_433.
This is not as complicated as it may sound at first
Option 2: Compile it yourself
Just follow the instructions from the BUILDING.md (exactly!) for you style of Linux - e.g. assuming Debian-like since you mentioned openHABian:
# first install some required libraries and software packages:
sudo apt-get install libtool libusb-1.0-0-dev librtlsdr-dev rtl-sdr build-essential autoconf cmake pkg-config
# if not yet installed, install git too (btw.: not mentioned in the BUILDING.md)
sudo apt-get install git
# go to your home directory:
cd ~
# make a copy (clone) of the current source code:
git clone https://github.com/merbanan/rtl_433.git
cd rtl_433/
mkdir build
cd build
# run cmake from inside the build directory (don't omit the ".."!)
cmake ..
# make it (compiles and linkes the rtl_433 binary)
make
# finally install the just compiled rtl_433:
make install
# test it (let it print out it command line parameters):
rtl_433 -h
Good luck.