fixed ambiguous grammatical construct as pointed out by user

Author: johnscancella

src/main/resources/MessageBundle.properties

@@ -72,7 +72,7 @@ required_tag_file_not_found_error=Required tag file [{}] was not found!
 tag_files_not_encoded_with_utf8_warning=Tag files are encoded with [{}]. We recommend always using UTF-8 instead.
 
 #For ManifestChecker.java
-bag_missing_tag_manifest_warning=Bag [{}] does not contain a tag manifest, which is always recommended.
+bag_missing_tag_manifest_warning=Bag [{}] does not contain a tag manifest. It is recommended to always include a tag manifest.
 different_case_warning=In manifest [{}], path [{}] is the same as another path except for the case. This can cause problems if moving the bag to a filesystem that is case insensitive.
 manifest_line_violated_spec_error=Manifest contains line [{}] which does not follow the specified form of <CHECKSUM> <PATH>
 md5sum_generated_line_warning=Path [{}] starts with a *, which means it was generated with a non-bagit tool. It is recommended to remove the * in order to conform to the Bagit specification.