add doc: how to add fonts

Add an example about how to add additional fonts indside the PlantUML docker container.

examples/README.md

@@ -1,5 +1,6 @@
 # Examples
 
+- [Additional fonts inside the PlantUML docker container](./additional-fonts)
 - [Nginx simple reverse proxy example](./nginx-simple)
 - [Nginx reverse proxy example with defined location directive (different context path)](./nginx-contextpath)
 - [Kubernetes simple deployment](./kubernetes-simple)

examples/additional-fonts/README.md

@@ -0,0 +1,73 @@
+# Additional fonts inside the PlantUML docker container
+
+It is possible to make additional fonts available to PlantUML by mapping them via a volume within the docker container.
+
+Since the base image from the docker container is using Ubuntu, fonts can easily be provided by just adding them somewhere inside the `~/.local/share/fonts` directory.
+
+**Tipp**: to not overwrite the container fonts add the additional files inside an own sub-folder, e.g., `custom` or `host`.
+
+In the following you can find an example how to provide all fonts of your host machine in the PlantUML docker container for Jetty and Tomcat.
+
+
+## Jetty
+
+In the case of the Jetty docker container the home directory is `/var/lib/jetty`.
+
+```yaml
+services:
+  plantuml-server:
+    image: plantuml/plantuml-server:jetty
+    container_name: plantuml-server
+    ports:
+      - "80:8080"
+    environment:
+      - TZ=Europe/Berlin
+      - BASE_URL=plantuml
+    volumes:
+      - /usr/share/fonts:/var/lib/jetty/.local/share/fonts/host:ro
+```
+
+
+## Tomcat
+
+In the case of the Tomcat docker container the home directory is `/root`.  
+_Yes, the tomcat container is running as `root` which is basically a really bad idea w.r.t. security. Create a pull request and maintain it if you want to change that._
+
+```yaml
+services:
+  plantuml-server:
+    image: plantuml/plantuml-server:tomcat
+    container_name: plantuml-server
+    ports:
+      - "80:8080"
+    environment:
+      - TZ=Europe/Berlin
+      - BASE_URL=plantuml
+    volumes:
+      - /usr/share/fonts:/root/.local/share/fonts/host:ro
+```
+
+
+## Verification
+
+The following command will print a list of all available fonts inside the docker container:
+
+```bash
+docker exec -it plantuml-server fc-list
+```
+
+To find a special font add a grep filter to the command:
+
+```bash
+docker exec -it plantuml-server fc-list | grep "<name-of-font>"
+```
+
+Naturally, it is also possible to check this via PlantUML itself by rendering the following diagram:
+
+```plantuml
+@startuml
+listfonts
+@enduml
+```
+
+**Note**: If you have added a lot of fonts: (a) this diagram may take a few seconds to generate, and (b) eventually the PNG image may be clipped. To avoid the latter, render the diagram as an SVG image.

examples/additional-fonts/docker-compose.yml

@@ -0,0 +1,13 @@
+version: "3"
+
+services:
+  plantuml-server:
+    image: plantuml/plantuml-server:jetty
+    container_name: plantuml-server
+    ports:
+      - "80:8080"
+    environment:
+      - TZ=Europe/Berlin
+      - BASE_URL=plantuml
+    volumes:
+      - /usr/share/fonts:/var/lib/jetty/.local/share/fonts/host:ro