Fleshed out readme

README.md

@@ -8,4 +8,35 @@
 * Windows: `scoop bucket add dynamo https://github.com/glassechidna/dynamo.git; scoop install dynamo`
 * Otherwise get the latest build from the [Releases][releases] tab.
 
+## Usage
+
+```
+dynamo table-name [partition key value [sort key value-or-expression]]
+```
+
+* If only a table name is specified, every row will be scanned.
+* If a table name and partition key are provided, either:
+  * That item will be returned (for single-key schemas)
+  * All matching items will be returned (for partition+sort key schemas)
+* If a table name, partition key and sort key are provided, only the matching
+  item will be returned.
+
+In place of a constant sort key, you can also type:
+
+* `> someval` - all items with sort key value greater than `someval`
+* `>= someval` - as above, but "greater than or equal to"
+* `<= someval` - as above, but "less than or equal to"
+* `< someval` - as above, but "less than"
+* `between val1 val2` - all items with sort keys between `val1` and `val2`
+* `someval*` - all items with sort keys that begin with `someval`
+
+By default, only **10** items will be returned -- this is to avoid accidentally
+downloading an entire table! This can be controlled with the `-n 30` flag.
+Passing `-n 0` disables the limit.
+
+Finally, output is pretty-printed and colourised when executed directly. If
+executed as part of a script (as determined by `isatty`), output will be
+one-item-per-line in [JSON Lines][jsonlines] format.
+
 [releases]: https://github.com/glassechidna/dynamo/releases
+[jsonlines]: http://jsonlines.org/