update README with correct behavior for fragment parameter

Author: bmjen

README.md

@@ -218,7 +218,7 @@ Specifies a file to read into the content of the fragment. **Note**: You must su
 
 #####`target`
 
-*Required.* Specifies the destination file of the fragment. Valid options: a string containing an absolute path.
+*Required.* Specifies the destination file of the fragment. Valid options: a string containing the title of the parent `concat` resource.
 
 ###Deprecations
 
@@ -280,4 +280,4 @@ For more information, see our [module contribution guide.](https://docs.puppetla
 
 ###Contributors
 
-To see who's already involved, see the [list of contributors.](https://github.com/puppetlabs/puppetlabs-concat/graphs/contributors)
+To see who's already involved, see the [list of contributors.](https://github.com/puppetlabs/puppetlabs-concat/graphs/contributors)