Add Version Specifiers to README

README.md

@@ -29,4 +29,18 @@ This will test the `MyFramework` scheme from the `MyFramework.xcodeproj` project
 | `platform` | Yes | `iOS` \| `macOS` \| `tvOS`| N/A | The platform to test on. |
 | `project` | Yes | `String` | N/A | The path to the project to test. |
 | `scheme` | Yes | `String` | N/A | The name of the scheme to test. |
-| `version` | No | `String` | `latest` | The OS version to test against. `latest` is a special case that will always use the latest available version. |
+| `version` | No | `String` | `latest` | See [version specifiers](#version-specifiers). |
+
+### Version Specifiers
+
+Special cases can be provided when specifying a version. These specifiers work against the **locally installed** versions, rather than the latest version published by Apple.
+
+| Case | Explanation |
+|------|-------------|
+| `latest` | The latest stable version |
+| `last-major` | The last major stable version, e.g. 10.x.x if the latest version is 11.x.x |
+| `last-minor` | The last minor stable version, e.g. 11.1.x if the latest version is 11.2.x |
+| `beta` | The latest beta version |
+| `11.3.1` | The exact version 11.3.1 |
+| `11.3` | The latest version 11.3 available (any patch) |
+| `11` | The latest version 11 available (any minor; any patch) |