Doc: how to install specific Micromamba version (#3517)

Co-authored-by: Johan Mabille <[email protected]>

docs/source/installation/micromamba-installation.rst

@@ -55,6 +55,11 @@ On Windows Powershell, use
 
    Invoke-Expression ((Invoke-WebRequest -Uri https://micro.mamba.pm/install.ps1).Content)
 
+A specific micromamba release can be installed by setting the ``VERSION`` environment variable.
+The release versions contain a build number in addition to the micromamba version.
+
+Micromamba releases can be found on Github: https://github.com/mamba-org/micromamba-releases/releases
+
 Self updates
 ^^^^^^^^^^^^
 Once installed, ``micromamba`` can be updated with