DOCS: Update usage section on commandline usage

Show correct way to specify output file in batch processing.
Fix help message in the commandline script showing the default format (is "txt", but help message said "csv").

docs/usage.rst

@@ -45,7 +45,7 @@ Command Line Use
 
 * To extract features from a batch run::
 
-    pyradiomics <path/to/input> <path/to/output>
+    pyradiomics <path/to/input>
 
 * The input file for batch processing is a CSV file where the first row is contains headers and each subsequent row
   represents one combination of an image and a segmentation and contains at least 2 elements: 1) path/to/image,
@@ -60,6 +60,13 @@ Command Line Use
 
     All headers should be unique and different from headers provided by PyRadiomics (``<filter>_<class>_<feature>``).
 
+* By default, results are printed out to the console window. To store the results in a CSV-structured text file, add the
+  ``-o <PATH>`` and ``-f csv`` arguments, where ``<PATH>`` specifies the filepath where the results should be stored.
+  e.g.::
+
+    pyradiomics <path/to/image> <path/to/segmentation> -o results.csv -f csv
+    pyradiomics <path/to/input> -o results.csv -f csv
+
 * Extraction can be customized by specifying a `parameter file <radiomics-parameter-file-label>` in the ``--param``
   argument and/or by specifying override settings (only `type 3 customization <radiomics-settings-label>`) in the
   ``--setting`` argument. Multiple overrides can be used by specifying ``--setting`` multiple times.

radiomics/scripts/__init__.py

@@ -58,11 +58,11 @@ def parse_args(custom_arguments=None):
                                 'invalid result (NaN)')
   outputGroup.add_argument('--format', '-f', choices=['csv', 'json', 'txt'], default='txt',
                            help='Format for the output.\n'
-                                '"csv" (Default): one row of feature names, followed by one row of\n'
-                                'feature values per case.\n'
+                                '"txt" (Default): one feature per line in format "case-N_name:value"\n'
                                 '"json": Features are written in a JSON format dictionary\n'
                                 '(1 dictionary per case, 1 case per line) "{name:value}"\n'
-                                '"txt": one feature per line in format "case-N_name:value"')
+                                '"csv": one row of feature names, followed by one row of\n'
+                                'feature values per case.')
   outputGroup.add_argument('--format-path', choices=['absolute', 'relative', 'basename'], default='absolute',
                            help='Controls input image and mask path formatting in the output.\n'
                                 '"absolute" (Default): Absolute file paths.\n'