Update changelog, mention requirement for PMD 6.27.0

Note: the pmd-core version we depend upon is actually still 6.23.0,
there are no binary API changes, just the tab size change.

Author: adangel

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## 6.27.0
 
+* This version of pmd-designer requires at least PMD 6.27.0 due to changes in tab size.
+* Adjust tab width char handling (refs [#45](https://github.com/pmd/pmd-designer/pull/45))
+
 See https://github.com/pmd/pmd-designer/milestone/12
 
 ## 6.24.0

README.md

@@ -28,7 +28,7 @@ If the `bin` directory of your PMD distribution is on your shell's path, then yo
 
 ### Updating
 
-The latest version of the designer currently **works with PMD 6.23.0 and above**.
+The latest version of the designer currently **works with PMD 6.27.0 and above**.
 You can simply replace `pmd-ui-6.X.Y.jar` with the [latest build](https://github.com/pmd/pmd-designer/releases/latest) in the installation folder of your
 PMD distribution.