contrib/Dockerfile: fix the build and improve the usage

Install a sample config, include a self-signed cert and setup a
local user and chroot.

.dockerignore

@@ -2,8 +2,10 @@
 !*.c
 !*.h
 !*.y
-!compat/*.c
-!compat/*.h
+!*.[1-9]
+!compat
 !have/*.c
 !Makefile
 !configure
+!contrib/Docker.gmid.conf
+!contrib/gencert

contrib/Docker.gmid.conf

@@ -0,0 +1,9 @@
+user gmid
+chroot "/var/gemini"
+
+server "localhost" {
+	listen on * port 1965
+	cert "/etc/ssl/localhost.pem"
+	key  "/etc/ssl/private/localhost.key"
+	root "/"
+}

contrib/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine as builder
+FROM alpine
 WORKDIR /build
 RUN apk update &&	\
 	apk upgrade &&	\
@@ -6,14 +6,14 @@ RUN apk update &&	\
 		alpine-sdk	\
 		linux-headers	\
 		bison		\
-		libretls-dev	\
-		libretls-static	\
-		libevent-dev	\
-		libevent-static
+		libevent-dev 	\
+		openssl-dev
 COPY . .
-RUN make static
-
-FROM alpine
-RUN apk update && apk upgrade
-COPY --from=builder /build/gmid /bin/gmid
-ENTRYPOINT ["gmid"]
+RUN ./configure && make && make install
+RUN adduser -H -S -s /sbin/nologin gmid
+RUN mkdir /var/gemini
+RUN ./contrib/gencert -e localhost && \
+	mv localhost.pem /etc/ssl && \
+	mv localhost.key /etc/ssl/private
+RUN mv contrib/Docker.gmid.conf /etc/gmid.conf
+ENTRYPOINT ["gmid", "-f"]

contrib/Makefile

@@ -1,4 +1,5 @@
 DISTFILES =	Makefile \
+		Docker.gmid.conf \
 		Dockerfile \
 		README \
 		gencert \