Update Dockerfile to add mermaid support

Dockerfile

@@ -43,6 +43,14 @@ RUN mkdir -p /opt/appbin
 RUN apk add --no-cache git openssl py-pygments libc6-compat g++
 #https://github.com/gohugoio/hugo/releases/download/v0.73.0/hugo_extended_0.73.0_Linux-64bit.tar.gz
 RUN wget https://github.com/gohugoio/hugo/releases/download/v${HUGO_VERSION}/hugo_extended_${HUGO_VERSION}_Linux-64bit.tar.gz -O - | tar -C /opt/appbin -xvzf - 
+
+## Install Mermaid CLI (along with pupeeter and Chromium)
+RUN apk add --no-cache npm \
+  && cd /root \
+  && npm install mermaid.cli
+
+ENV PATH="${PATH}:/root/node_modules/.bin"
+
 RUN export uid=1000 gid=1000 && \
     echo "appuser:x:${uid}:${gid}:AppUser,,,:/opt/course_builder:/bin/bash" >> /etc/passwd && \
     echo "appuser:x:${uid}:" >> /etc/group && \