Unique exit codes

Implemented Uniquie exit codes for the following exits:

Exit code	Reason	Solution
10	Call of 'archspec cpu' failed	Please install archspec, for example via 'pipx install archspec'
20	Requested package set is not available	Use 'available' command to see list of available package_sets
30	Current directory is already initialised	Check if you are in the right directory
40	Current directory is not initialised	Check if you are in the right directory, if so use 'init' command to initialise

Skipped the changes to 1) remove command as its not yet implemented 2) sanity check for mpsd_release as its removed in one of the MR.

Closes #29 (closed)

development.rst

@@ -17,3 +17,20 @@ Then every time you commit, pre-commit will run all checks defined in `.pre-comm
 you can run the pre-commit checks manually by running::
 
     pre-commit run --all-files
+
+Debugging exit codes
+--------------------
+Non zero exit codes are used to indicate that the program exited due to an error.
+There are multiple ways to debug this. You could run the program with more verbose logging::
+
+    mpsd-software -l debug ...
+
+Here is a list of exit codes and what they mean:
++-----------+------------------------------------------+----------------------------------------------------------------------------------+
+| Exit code | Reason                                   | Solution                                                                         |
++===========+==========================================+==================================================================================+
+| 10        | Call of 'archspec cpu' failed            | Please install archspec, for example via 'pipx install archspec'                 |
+| 20        | Requested package set is not available   | Use 'available' command to see list of available package_sets                    |
+| 30        | Current directory is already initialised | Check if you are in the  right directory                                         |
+| 40        | Current directory is not initialised     | Check if you are in the  right directory, if so use 'init' command to initialise |
++-----------+------------------------------------------+----------------------------------------------------------------------------------+