Add CHANGELOG.md to document project updates and enhance README.md with changelog reference.

Author: fknierim

CHANGELOG.md

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+# Changelog
+
+<!-- markdownlint-disable MD024-->
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+<!-- changelog -->
+
+## [Unreleased]
+
+### Added
+
+- C4 level definitions and styling
+
+### Changed
+
+- Default font changed to "Arial"
+- Refactored skin parameters across multiple theme files for consistency
+- Updated border color settings for C4 levels to 'none'
+- Improved example files with local input files and consistent include paths
+- Enhanced mind map styling with style enhancements
+
+### Fixed
+
+- Node borders fixed
+- Removed duplicate and deprecated settings across theme files
+- Improved spacing and layout settings
+
+## [1.3.0] - 2025-06-11
+
+### Changed
+
+- Updated layout settings and skin parameters across multiple PUML theme files
+
+## [1.2.0] - 2025-04-14
+
+### Added
+
+- Mind map style adjustments and enhancements
+- Complete include URL examples (commented for direct visibility)
+- .gitignore file
+- Diagram hints for better usability
+
+### Changed
+
+- Linked examples in README.md for better navigation
+- Corrected spacing in various theme files
+
+### Fixed
+
+- Fixed node borders in diagrams
+
+## [1.1.0] - 2024-04-23
+
+### Changed
+
+- Font changed from "Arial" to "Helvetica" for better consistency
+
+### Fixed
+
+- Multiple sequence diagram theme updates and improvements
+
+## [1.0.0] - 2024-01-04
+
+### Added
+
+- Initial PlantUML theme collection for doubleSlash CI styling
+- Use case diagram theme (`puml-theme-doubleslash-usecase.puml`)
+- Activity diagram theme (`puml-theme-doubleslash-activity.puml`) with piprocess support
+- System diagram theme for C4 level 1 and 2 (`puml-theme-doubleslash-system.puml`)
+- Class diagram theme, also supports ER-diagrams (`puml-theme-doubleslash-class.puml`)
+- Sequence diagram theme (`puml-theme-doubleslash-sequence.puml`)
+- Gantt diagram theme (`pgantt-theme-doubleslash.puml`)
+- Mind map theme (`puml-theme-doubleslash-mindmap.puml`)
+- General theme file (`puml-theme-doubleslash-general.puml`)
+- Main theme file (`puml-theme-doubleslash.puml`)
+- Initial `doubleslash_style.theme` file
+- README with comprehensive usage instructions and examples
+- Support for 7 different diagram types with examples
+
+### Changed
+
+- Font standardized to Helvetica across all themes
+- Multiple refinements to styling parameters throughout development
+- Timeline font size adjusted to 12 for better readability
+- Various color and layout optimizations
+
+### Fixed
+
+- Consistent styling across all diagram types established
+- Theme parameter conflicts resolved
+
+[Unreleased]: https://github.com/doubleSlashde/umltheme/compare/v1.3.0...HEAD
+[1.3.0]: https://github.com/doubleSlashde/umltheme/compare/v1.2.0...v1.3.0
+[1.2.0]: https://github.com/doubleSlashde/umltheme/compare/v1.1.0...v1.2.0
+[1.1.0]: https://github.com/doubleSlashde/umltheme/compare/v1.0.0...v1.1.0
+[1.0.0]: https://github.com/doubleSlashde/umltheme/releases/tag/v1.0.0

README.md

@@ -1,42 +1,62 @@
 # umltheme
+
 This repo contains doubleSlash CI styling information to include in plantUML drawings
 Use stylings by including the theme file at the top of your code.
+
+## Changelog
+
+The changelog is maintained in [CHANGELOG.md](./CHANGELOG.md). For the latest version, see [releases](https://github.com/doubleSlashde/umltheme/releases).
+
+## Supported themes
+
 ### Include for use case diagram
-```
+
+``` txt
 !include https://raw.githubusercontent.com/doubleSlashde/umltheme/main/puml-theme-doubleslash-usecase.puml
 ```
+
 ### Include for activity diagram
-```
+
+``` txt
 !include https://raw.githubusercontent.com/doubleSlashde/umltheme/main/puml-theme-doubleslash-activity.puml
 ```
+
 ### Include for system diagram (C4 level 1 and 2)
-```
+
+``` txt
 !include https://raw.githubusercontent.com/doubleSlashde/umltheme/main/puml-theme-doubleslash-system.puml
 ```
+
 ### Include for class diagram (also for ER-diagrams)
-```
+
+``` txt
 !include https://raw.githubusercontent.com/doubleSlashde/umltheme/main/puml-theme-doubleslash-class.puml
 ```
-### Include for sequence diagram 
-```
+
+### Include for sequence diagram
+
+``` txt
 !include https://raw.githubusercontent.com/doubleSlashde/umltheme/main/puml-theme-doubleslash-sequence.puml
 ```
 
 ### Include for Gantt diagram
-```
+
+``` txt
 @startgantt
 !include https://raw.githubusercontent.com/doubleSlashde/umltheme/main/pgantt-theme-doubleslash.puml
 ...
 ```
 
 ### Include for mind map
-```
+
+``` txt
 @startmindmap
 !include https://raw.githubusercontent.com/doubleSlashde/umltheme/main/puml-theme-doubleslash-mindmap.puml
 ...
 ```
 
 ## Support for the following diagrams
+
 1. Use Cases (see [examples/usecase.puml](examples/usecase.puml)): diagram to support documentation of PEOPLE and PROCESS.
 2. Activity (see [examples/activity_model.puml](examples/activity_model.puml)): diagram to illustrate activities in a PROCESS. It can be used as an alternative to BPMN diagrams.  
 3. System model (see [examples/systemmodel.puml](examples/systemmodel.puml)): diagram for a functional SYSTEM view. Represents the first two layers of a C4 model (System context and Containers)