Merge branch 'develop' into 'master'

Detail the interplay between latest and previous

See merge request !65

README.md

@@ -42,6 +42,17 @@ source deactivate
 
 (Nesh: `smomw122`; HLRN: `shkifmwr`; Geomar: `wrath`)
 
+## A note on stability
+
+The environments are updated frequently (but irregularly).  This comes with a
+catch:  Updating an environment potentially introduces problems that are not
+immediately visible when testing the updated installation.  To at least
+partially make up for this, the state of the environments _before_ an update is
+copied to `<willis_home_dir>/TM/software/miniconda3_previous`.  So if you
+suddenly run into problems in an environment that used to work.  Switch to
+`miniconda3_previous` and check if this helps.  If you find problems, please
+[file an issue here][issues].
+
 ## Using the environments on nb.geomar.de
 
 There is an installer which allows for adding kernels using these environments