Address PR comment

Author: mcbarton

docs/source/InstallationAndUsage.rst

@@ -22,6 +22,7 @@ this environment with mamba by executing the following
 .. code-block:: bash
 
     micromamba create -f environment-dev.yml
+    micromamba activate xeus-cpp
     micromamba install jupyterlab -c conda-forge
 
 Now you can compile the kernel from the source by executing (replace `$CONDA_PREFIX`