Update BUILDING.md

BUILDING.md

@@ -1,6 +1,8 @@
-# Building PlantUML with Gradle
+# Building PlantUML
 
-Thank you for your interest in contributing to PlantUML! This guide will help you build the PlantUML project using Gradle.
+Thank you for your interest in contributing to PlantUML! This guide will help you build the PlantUML project.
+
+# Building PlantUML with Gradle
 
 ## Prerequisites
 
@@ -67,3 +69,39 @@ After successfully building the project, you are ready to start contributing to
 If you encounter any issues while building the project, feel free to ask for help on the [PlantUML Community Forum](https://forum.plantuml.net/) or open an issue on the [GitHub repository](https://github.com/plantuml/plantuml/issues).
 
 Thank you for contributing to PlantUML!
+
+## Building PlantUML with Ant (Alternative Method)
+
+For those who prefer using Ant, or only have access to Ant, we provide a `build.xml` Ant build script as a fallback option to build PlantUML.
+
+### Prerequisites
+
+Ensure that you have the following installed on your system:
+
+- [Java Development Kit (JDK)](https://jdk.java.net/) - version 8 or newer
+- [Apache Ant](https://ant.apache.org/bindownload.cgi) - to run the build script
+- [Git](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git) - to clone the repository and manage the version control
+
+### Getting the Source Code
+
+Clone the PlantUML repository to your local system. You can clone the repository by running the following command in your terminal or command prompt:
+
+```sh
+git clone https://github.com/plantuml/plantuml.git
+```
+
+Navigate to the directory containing the `build.xml`:
+
+```sh
+cd plantuml
+```
+
+### Building the Project
+
+To build the project using Ant, run the following command:
+
+```sh
+ant
+```
+
+If you have Ant set up correctly and the prerequisites are met, the build process should start, and the project will be built based on the instructions in the `build.xml`.