Fixes #552 Add missing readme entry for generateReleaseNotesPreviousTag

Author: ncipollo

README.md

@@ -25,6 +25,7 @@ This action will create a GitHub release and optionally upload an artifact to it
 | discussionCategory         | When provided this will generate a discussion of the specified category. The category must exist otherwise this will cause the action to fail. This isn't used with draft releases. The default "Announcements" category is not supported via the API and will cause an error if used here. | false      | ""                   |
 | draft                      | Optionally marks this release as a draft release. Set to true to enable.                                                                                                                                                                                                                    | false      | ""                   |
 | generateReleaseNotes       | Indicates if release notes should be automatically generated.                                                                                                                                                                                                                               | false      | false                |
+| generateReleaseNotesPreviousTag | An optional previous tag to use when generating release notes. This will limit the release notes to changes between the two tags.                                                                                                                                                       | false      | ""                   |
 | immutableCreate            | Indicates if immutable release creation should be used. When enabled, the action will first create a draft, upload artifacts, then publish the release.                                                                                                                                     | false      | false                |
 | makeLatest                 | Indicates if the release should be the "latest" release or not. legacy specifies that the latest release should be determined based on the release creation date and higher semantic version.                                                                                               | false      | "legacy"             |
 | name                       | An optional name for the release. If this is omitted the tag will be used.                                                                                                                                                                                                                  | false      | ""                   |