新增learn-kubernetes（https://github.com/yyong-brs/learn-kubernetes）相关文件

learn/learn-kubernetes-master/kiamol/ch15/docker-images/cert-generator/Dockerfile

@@ -0,0 +1,15 @@
+FROM alpine:3.12
+
+RUN apk add --no-cache openssl
+RUN apk add --no-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing kubectl
+
+COPY start.sh /
+RUN chmod +x /start.sh
+
+ENV HOST_NAME="kiamol.local" \
+    HOST_IP="127.0.0.1" \
+    SAN="DNS:hello.kiamol.local,DNS:vweb.kiamol.local,DNS:todo.kiamol.local,DNS:todo2.kiamol.local,DNS:pi.kiamol.local" \
+    EXPIRY_DAYS=730
+
+WORKDIR /certs
+CMD /start.sh ${HOST_NAME} ${HOST_IP} ${SAN} ${EXPIRY_DAYS}