docs: added developers' installation

Author: fstagni

docs/user/reference/known-installations.md

@@ -7,9 +7,9 @@ This page shows an incomplete list of DiracX installations in alphabetical order
 
     If your installation is missing, please use the edit button in the top right to add it!
 
-# LHCb
+## LHCb
 
-[LHCb](https://lhcb-outreach.web.cern.ch/) is one of the four large experiments of the Large Hadron Collider at CERN and DiracX is used for all of their distributed computing activities.
+[LHCb](https://lhcb-outreach.web.cern.ch/){target="_blank"} is one of the four large experiments of the Large Hadron Collider at CERN and DiracX is used for all of their distributed computing activities.
 
 === "Client setup"
 
@@ -37,3 +37,12 @@ This page shows an incomplete list of DiracX installations in alphabetical order
     ```bash
     export DIRACX_URL=https://lhcbdiracx.app.cern.ch/
     ```
+
+# Developers' installation
+
+We provide a developers' installation at https://diracx-cert.app.cern.ch/. The installation is mostly used for testing and certifying candidate releases.
+
+The installation uses the [`dteam` Virtual Organization](https://dteam-auth.cern.ch/){target="_blank"} and as such is used to access Grid resources. The installation is using the latest pre-release of DiracX and as such can not be considered a stable and fully reliable installation. If nevertheless:
+- you are part of `dteam` (becoming member is an easy process)
+- you would like to access an existing DiracX installation, and see it "in action"
+[get in contact](https://web.diracgrid.org/contacts.html) explaining your use-case.