add docs

README.rst

@@ -5,3 +5,20 @@
  A CLI for creating on-disk directory hierarchies based on Excel columns
 -------------------------------------------------------------------------
 
+Usage:
+
+```
+# Subdirectory groupings
+poetry run python xlsx_dir_map -i "Folder Name List.xlsx" -o "output_subdirs" -r "A2:D340" A B C D
+
+# Flat directory groupings
+poetry run python xlsx_dir_map -i "Folder Name List.xlsx" -o "output_flatdirs" -r "A2:D340" A:B:C:D
+```
+
+The command above specifies the name of an input spreadsheet (`-i`), the root of the outputs (`-o`),
+and a range of spreadsheet cells to parse (`-r`). Then, the CLI accepts an arbitrary number of column
+group arguments.
+
+The column group arguments specify subdirectory grouping structures. Column names separated by a space
+will create an additional nested directory `/output/.../A/B` whereas column names separated by a colon
+will create a directory whose name contains the values of both columns, i.e `/output/.../A B`. 

xlsx_dir_map/__main__.py

@@ -1,6 +1,6 @@
 import argparse
 
-parser = argparse.ArgumentParser(description='Process some intzzz')
+parser = argparse.ArgumentParser(description='Convert spreadsheet data into named directories')
 parser.add_argument('--in', '-i', dest='file_in', required=True)
 parser.add_argument('--out', '-o')
 parser.add_argument('--range', '-r', dest='cell_range')