include prepare and reinstall in help string

- reinstall needs to know toolchain(s) as well.

mpsd-software-environment.py

@@ -380,9 +380,11 @@ def main():
 
         else:
             subp.add_argument(
-                "release", type=str, help="Release version to install or remove"
+                "release",
+                type=str,
+                help="Release version to prepare, install, reinstall or remove",
             )
-            if cmd in ["install", "reinstall"]:
+            if cmd in ["install", "reinstall", "remove"]:
                 # "install" command needs additional documentation
                 if cmd == "install":
                     help_part2 = (