Build mono docker image and update docs

mono.Dockerfile

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+FROM mono:latest
+LABEL author="artur@barichello.me,asheraryam@gmail.com"
+
+
+USER root
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ca-certificates \
+    git \
+    python \
+    python-openssl \
+    unzip \
+    wget \
+    zip \
+    && rm -rf /var/lib/apt/lists/*
+
+# When in doubt see the downloads page
+# https://downloads.tuxfamily.org/godotengine/
+ENV GODOT_VERSION "3.2.1"
+
+# Example values: stable, beta1, rc2, alpha3, etc.
+# Also change the SUBDIR property when NOT using stable
+ENV RELEASE_NAME "stable"
+
+# This is only needed for non-stable builds (alpha, beta, RC)
+# e.g. SUBDIR "/beta1"
+ENV SUBDIR "" 
+
+RUN wget https://downloads.tuxfamily.org/godotengine/${GODOT_VERSION}${SUBDIR}/mono/Godot_v${GODOT_VERSION}-${RELEASE_NAME}_mono_linux_headless_64.zip \
+    && wget https://downloads.tuxfamily.org/godotengine/${GODOT_VERSION}${SUBDIR}/mono/Godot_v${GODOT_VERSION}-${RELEASE_NAME}_mono_export_templates.tpz
+
+RUN mkdir ~/.cache \
+    && mkdir -p ~/.config/godot \
+    && mkdir -p ~/.local/share/godot/templates/${GODOT_VERSION}.${RELEASE_NAME}.mono \
+    && unzip Godot_v${GODOT_VERSION}-${RELEASE_NAME}_mono_linux_headless_64.zip \
+    && mv Godot_v${GODOT_VERSION}-${RELEASE_NAME}_mono_linux_headless_64/Godot_v${GODOT_VERSION}-${RELEASE_NAME}_mono_linux_headless.64 /usr/local/bin/godot \
+    && mv Godot_v${GODOT_VERSION}-${RELEASE_NAME}_mono_linux_headless_64/GodotSharp /usr/local/bin/GodotSharp \
+    && unzip Godot_v${GODOT_VERSION}-${RELEASE_NAME}_mono_export_templates.tpz \
+    && mv templates/* ~/.local/share/godot/templates/${GODOT_VERSION}.${RELEASE_NAME}.mono \
+    && rm -f Godot_v${GODOT_VERSION}-${RELEASE_NAME}_mono_export_templates.tpz Godot_v${GODOT_VERSION}-${RELEASE_NAME}_mono_linux_headless_64.zip
+
+ADD getbutler.sh /opt/butler/getbutler.sh
+RUN bash /opt/butler/getbutler.sh
+RUN /opt/butler/bin/butler -V
+
+ENV PATH="/opt/butler/bin:${PATH}"