docs: update README to include some clarification about the software folder

.gitmodules

@@ -38,5 +38,8 @@
 	path = boundary_conditions/PISM_38ka
 	url = https://gitlab.awi.de/paleodyn/boundary-conditions/pism_38ka.git
 [submodule "software/esm_tools"]
-	path = software/esm_tools
+	path = software/github.com/esm-tools/esm_tools
 	url = https://github.com/esm-tools/esm_tools
+[submodule "software/github.com/direnv/direnv"]
+	path = software/github.com/direnv/direnv
+	url = git@github.com:direnv/direnv.git

README.md

@@ -80,7 +80,7 @@ esm_master comp-awiesm-2.1
 
 7. Install the `direnv` program and connect it to your shell. That will allow you to set "per project" environmental variables, and do some checks as soon as you go to the model folder. All of the run configurations are designed to be locally contained within in
 the project folder, as is identified with the environmental variable
-${PROJECT_BASE}. This can be automatically set for you when you change into
+`${PROJECT_BASE}`. This can be automatically set for you when you change into
 the folder by using the direnv program. Source code of this program is delivered
 with the remaining source code under the software/github.com/direnv/direnv/
 folder. A pre-compiled, ready-to-use version for DKRZ's mistral is under
@@ -119,7 +119,11 @@ may have been updated.
 * `preliminary_experiments`: Experiments performed so that scientifically
   useful ones can follow, e.g. stepwise adjustment to a new orogaphy.
 * `software`: Helper software used for this project, e.g. the boundary
-  condition creator.
+  condition creator. This is organized in such a way that the URL you would use
+  to run `git clone` has the exact same form as the actual helper software. For
+  examle, esm-tools is officially hosted under
+  https://github.com/esm-tools/esm_tools. In the software folder, it is
+  therefore under `./software/github.com/esm-tools/esm_tools`.
 * `nonstandard_pool_files`: Files that might be needed in FESOM, but are not in
   the standard Mistral pool.
 * `utils`: Various utility scripts that may come in handy. Read the headers,

direnv @ 8e531391

+Subproject commit 8e53139148945df922fd00b85bbdd0694554ec9b