Add documentation for unit tests

doc/TESTBenches.md

@@ -109,6 +109,7 @@ information on how the images are built.
   - build image from `Dockerfile.clang.rhel9` (compilation only, artifacts not used currently)
 - [RAN-Ubuntu18-Image-Builder](https://jenkins-oai.eurecom.fr/job/RAN-Ubuntu18-Image-Builder/)
   ~BUILD-ONLY ~4G-LTE ~5G-NR
+  - run formatting check from `ci-scripts/docker/Dockerfile.formatting.bionic`
   - obelix: Ubuntu 20 image build using docker (Note: builds U20 images while pipeline is named U18!)
   - base image from `Dockerfile.base.ubuntu20`
   - build image from `Dockerfile.build.ubuntu20`, followed by
@@ -118,6 +119,7 @@ information on how the images are built.
     - target image from `Dockerfile.nrUE.ubuntu20`
     - target image from `Dockerfile.lteUE.ubuntu20`
     - target image from `Dockerfile.lteRU.ubuntu20`
+  - build unit tests from `ci-scripts/docker/Dockerfile.unittest.ubuntu20`, and run them
 
 #### Image Test pipelines