Dockerfile: Add tmux and libncurses-dev

Needed for devshell and menuconfig targets.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

Dockerfile

@@ -16,7 +16,8 @@ RUN apt-get install --no-install-recommends -y \
                        tar bzip2 curl dosfstools mtools parted \
                        syslinux tree python3-pip bc python3-yaml \
                        lsb-release python3-setuptools ssh-client \
-                       vim less mercurial iproute2 xz-utils gnupg && \
+                       vim less mercurial iproute2 xz-utils gnupg \
+                       tmux libncurses-dev && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*