Added simple usage to README file

README.md

@@ -1,7 +1,32 @@
-GW trigfind
-===========
+# GW trigfind
 
 A utility to find GW trigger files produced by event trigger generators and archived on the LIGO Data Grid.
 
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+
+## Quickstart for python
+
+To discover trigger files for a given channel:
+
+```python
+>>> from trigfind import find_trigger_files
+>>> cache = find_trigger_files(channel, etg, gpsstart, gpsend)
+```
+
+The resulting cache can then be read easily into a table using [`gwpy`](//gwpy.github.io/):
+
+```python
+>>> from gwpy.table import EventTable
+>>> t = EventTable.read(cache, format='ligolw.sngl_burst')
+```
+
+The format argument depends on the etg you use, but is likely to be one of `'ligolw.sngl_burst'`, `'ligolw.sngl_inspiral'`, or `'root'`.
+
+## Quickstart for command-line
+
+The same query can be performed from the command line by passing each of the functional arguments above as arguments to the `trigfind` executable script:
+
+```bash
+trigfind <channel> <etg> <gpsstart> <gpsend>
+```