It is better not index instruction in robots.txt file
By using webmaster tool, we can easily index or noindex the URL's with the help of robot file where we can tell crawlers to index which urls.
Add the meta-element robots to the source code of the page which is not supposed to appear in the index and set the value to NOINDEX.
By adding the following to the source code of a page, it will be removed from the index:
<meta name="robots" content="noindex">