adding the is_json tool and associated readme.md details

plugins/jsontools/README.md

@@ -5,10 +5,11 @@ Handy command line tools for dealing with json data.
 ## Tools
 
 - **pp_json** - pretty prints json
+- **is_json** - returns true if valid json; false otherwise
 
-## Usage
+## Examples
 
-##### pp_json - examples
+##### pp_json
 
 ```sh
 # curl json data and pretty print the results
@@ -19,4 +20,16 @@ less data.json | pp_json
 
 # json data directly from the command line
 echo '{"b":2, "a":1}' | pp_json
+```
+
+##### is_json
+```sh
+# curl json data and pretty print the results
+curl https://coderwall.com/bobwilliams.json | is_json
+
+# pretty print the contents of an existing json file
+less data.json | is_json
+
+# json data directly from the command line
+echo '{"b":2, "a":1}' | is_json
 ```