Fix some small documentation inconsistencies

README.md

@@ -1049,7 +1049,8 @@ previous section, with the following differences:
 
 * The `exprFile` is also used for specifying the process model to deploy from,
   but a notable difference is that for mutable containers this model is copied
-  into the container and deployed from within the container.
+  into the container and deployed from within the container. If the `exprFile`
+  parameter is omitted, an empty configuration is deployed.
 * To make deploying process models model possible that also use
   `nixproc-id-assign` to automatically assign unique numeric IDs, the
   `idResourcesFile` and `idsFile` parameters can be used to copy these models

nixproc/create-image-from-steps/steps/bootstrap-init.nix

@@ -10,12 +10,14 @@ result // pkgs.lib.optionalAttrs (!(input ? bootstrap) || input.bootstrap) {
     cat > /bin/bootstrap <<EOF
     #! ${pkgs.stdenv.shell} -e
 
-    # Add nix channel configuration
+    # Configure Nix channels
     nix-channel --add ${channelURL}
     nix-channel --update
+
+    # Deploy the processes model (in a child process)
     nixproc-${input.processManager}-switch &
 
-    # Overwrite the bootstrap script, so that it simply just starts the process manager
+    # Overwrite the bootstrap script, so that it simply just starts the process manager the next time we start the container
     cat > /bin/bootstrap <<EOR
     #! ${pkgs.stdenv.shell} -e
     exec ${cmd}