Updata after NV comments.

docs/user_docs/data_conversion.rst

@@ -21,6 +21,8 @@ The authors of the tool are happy to provide additional conversion routines if s
 Use of spec2nii 
 ---------------
 
+The specific sub command (e.g. `twix` or `dicom`) must be the first argument.
+
 To specify the creation of a JSON metadata file alongside a NIfTI file (recommended) use the :code:`-j` option with any other inputs. 
 
 File names can be specified with the :code:`-f` option and output directories with the :code:`-o` option.  

docs/user_docs/quick_start.rst

@@ -15,7 +15,7 @@ Before running FSL-MRS time domain data must be prepared in a complex 4D-NIFTI o
 
 Example conversion::
 
-    spec2nii -f my_metab_file dicom -j metab.dcm
+    spec2nii dicom -f my_metab_file -j metab.dcm
 
 This will convert the dicom file (metab.dcm) to a NIfTI file named my_metab_file.nii and because the -j option was specified, a JSON file called my_metab_file.json.