add fish shell testing container

fish/Dockerfile

@@ -0,0 +1,11 @@
+FROM debian:wheezy
+MAINTAINER Jessica Frazelle <jess@docker.com>
+
+RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-key D880C8E4 \
+    && echo 'deb http://download.opensuse.org/repositories/shells:/fish:/release:/2/Debian_7.0/ ./' > /etc/apt/sources.list.d/fish-shell.list \
+    && apt-get update && apt-get install -y \
+    fish \
+    --no-install-recommends \
+    && mkdir -p /root/.config/fish/completions
+
+ENTRYPOINT [ "fish" ]