fixed typo in help doc, added blob2.json for tests

Author: rsdoiel

cmds/jsoncols/jsoncols.go

@@ -27,7 +27,7 @@ returning the results in columns.  This is helpful in flattening content
 extracted from JSON blobs.  The default delimiter for each value
 extracted is a comma. This can be overridden with an option.
 
-+ EXPRESSION can be an empty stirng or dot notation for an object's path
++ EXPRESSION can be an empty string or dot notation for an object's path
 + INPUT_FILENAME is the filename to read or a dash "-" if you want to
   explicitly read from stdin
 	+ if not provided then %s reads from stdin

how-to/jsoncols/blob2.json

@@ -0,0 +1 @@
+{"name":"Fred","id":1,"counts":[10,9,8,7],"map":{"one":1,"two":2,"three":3}}