Add runtime instructions

Adds instructions for installing dependencies and optional environment
variables that might help users.

README.rst

@@ -28,12 +28,22 @@ How can I contribute?
 What do I need to contribute?
 -----------------------------
 
-* A host with python 3.6+, gcc and the python development header files
-* tox
-* go
+* A host with `python` 3.6+ and `tox`
 * docker and/or podman+buildah
 * vagrant (optional, can be used to test FIPS mode and registered hosts)
 
+Test setup on openSUSE
+^^^^^^^^^^^^^^^^^^^^^^
+
+To setup the test environment on openSUSE Leap 15.6 and Tumbleweed, run the following commands:
+
+
+.. code-block:: shell-session
+
+    # zypper -n in podman buildah docker git-core python3 python3-pip
+    # pip3 --quiet install --upgrade pip
+    # pip3 --quiet install tox --ignore-installed six
+
 How can I run the tests?
 ------------------------
 
@@ -43,6 +53,17 @@ How can I run the tests?
    will reduce the danger of race conditions when building containers)
 4. Run ``tox -e $language_stack -- -n auto``
 
+Environment variables
+^^^^^^^^^^^^^^^^^^^^^
+
+One can use the following environment variables to configure the behaviour of the BCI-Tests
+
+.. code-block:: shell-session
+
+    # export OS_VERSION=15.6                         # Target SLES version
+    # export CONTAINER_RUNTIME=podman                # Defaults to podman
+    # export TARGET=ibs-cr                           # ibs-cr = ToTest, ibs = Released, obs = Tumbleweed
+
 Technical contributions
 -----------------------