system/utils: Update README.md
system/utils: Update README.md

- Adds description of 'echo' command.
- Modifies description of 'cat' command.

Signed-off-by: Lokesh B V <a10c1c2561c872cd1fd5899c4340d5ec87a91507@partner.samsung.com>

Samsung/TizenRT,junmin-kim/TizenRT,jeongchanKim/TizenRT,JeonginKim/TizenRT,sunghan-chang/TizenRT,junmin-kim/TizenRT,junmin-kim/TizenRT,pillip8282/TizenRT,sunghan-chang/TizenRT,JeonginKim/TizenRT,an4967/TizenRT,an4967/TizenRT,jsdosa/TizenRT,sunghan-chang/TizenRT,jeongchanKim/TizenRT,HONGCHAEHEE/TizenRT,jeongarmy/TizenRT,HONGCHAEHEE/TizenRT,davidfather/TizenRT,pillip8282/TizenRT,junmin-kim/TizenRT,chanijjani/TizenRT,Samsung/TizenRT,jsdosa/TizenRT,chanijjani/TizenRT,sunghan-chang/TizenRT,jsdosa/TizenRT,jeongarmy/TizenRT,sunghan-chang/TizenRT,chanijjani/TizenRT,davidfather/TizenRT,davidfather/TizenRT,an4967/TizenRT,an4967/TizenRT,jsdosa/TizenRT,HONGCHAEHEE/TizenRT,Samsung/TizenRT,JeonginKim/TizenRT,JeonginKim/TizenRT,jeongchanKim/TizenRT,an4967/TizenRT,jeongarmy/TizenRT,Samsung/TizenRT,jsdosa/TizenRT,chanijjani/TizenRT,jeongchanKim/TizenRT,jeongarmy/TizenRT,pillip8282/TizenRT,HONGCHAEHEE/TizenRT,jeongchanKim/TizenRT,Samsung/TizenRT,junmin-kim/TizenRT,chanijjani/TizenRT,pillip8282/TizenRT,HONGCHAEHEE/TizenRT,Samsung/TizenRT,chanijjani/TizenRT,jsdosa/TizenRT,an4967/TizenRT,JeonginKim/TizenRT,an4967/TizenRT,davidfather/TizenRT,davidfather/TizenRT,davidfather/TizenRT,Samsung/TizenRT,jeongchanKim/TizenRT,chanijjani/TizenRT,pillip8282/TizenRT,davidfather/TizenRT,sunghan-chang/TizenRT,HONGCHAEHEE/TizenRT,sunghan-chang/TizenRT,jeongarmy/TizenRT,jeongchanKim/TizenRT,junmin-kim/TizenRT,JeonginKim/TizenRT,junmin-kim/TizenRT,pillip8282/TizenRT,jeongarmy/TizenRT,jeongarmy/TizenRT,pillip8282/TizenRT,jsdosa/TizenRT