Added a recommendation to use Mamba (#4622)

* Added a recommendation to use Mamba

* Added missing new line

* Fixed update instructions

README.md

@@ -78,18 +78,21 @@ This installation guide is for ISIS users interested in installing ISIS (3.6.0)+
 
         conda config --env --add channels usgs-astrogeology
 
+6.  Download [Mamba](https://github.com/mamba-org/mamba). The ISIS environment is quite large and the Conda solver can take hours to resolve it. Instead, we recommend you use the much faster [Mamba](https://github.com/mamba-org/mamba) solver:
 
-6.  The environment is now ready to download ISIS and its dependencies:
+        conda install -c conda-forge mamba
 
-        conda install -c usgs-astrogeology isis
+7.  The environment is now ready to download ISIS and its dependencies:
+
+        mamba install -c usgs-astrogeology isis
 
     If you would like to work with our latest ISIS version 3, rather than updating
     to ISIS 4, instead run:
 
-	    conda install -c usgs-astrogeology isis=3.10.0
+	    mamba install -c usgs-astrogeology isis=3.10.0
 
 
-7.  Finally, setup the environment variables:
+8.  Finally, setup the environment variables:
 
     ISIS requires several environment variables to be set in order to run correctly.
     The variables include: ISISROOT and ISISDATA.
@@ -147,6 +150,8 @@ This installation guide is for ISIS users interested in installing ISIS (3.6.0)+
 
       The environment variables are now set and ISIS is ready for use every time the isis environment is activated.
 
+      **Note** This method will not enable tab completion for arguments in C-Shell.
+
 
 
 ### Installation with Docker
@@ -316,16 +321,16 @@ remove these elements to and from your path.
 
 ### Updating
 
-  To update to a new version of ISIS up to version 3.9.1, simply run `conda update isis3`
+  To update to the newest version of ISIS, run `mamba update -c usgs-astrogeology isis`
 
-  To update to our latest release candidate up to version 3.9.1, run `conda update -c usgs-astrogeology -c usgs-astrogeology/label/RC isis3`
+  To update to our latest release candidate , run `mamba update -c usgs-astrogeology/label/RC isis`
 
   Note that for ISIS versions 3.10 and above, new versions and release candidates will only be
-  available under the package name `isis` and `conda update isis3` and  
-  `conda update -c usgs-astrogeology -c usgs-astrogeology/label/RC isis3`
-  will no longer work for additional updates. Instead, after installing an `isis` package,
-  `conda update isis` should be used to update to a new version and
-  `conda update -c usgs-astrogeology/label/RC isis` to update to a new release candidate.
+  available under the package name `isis` and `mamba update isis3` and
+  `mamba update -c usgs-astrogeology -c usgs-astrogeology/label/RC isis3`
+  will not work for additional updates. Instead, after installing an `isis` package,
+  `mamba update isis` should be used to update to a new version and
+  `mamba update -c usgs-astrogeology/label/RC isis` to update to a new release candidate.
 
 ### Operating System Requirements