added readme and changed Dockerfile

Dockerfile

@@ -7,8 +7,12 @@ LABEL Description="This image is used to learn building dockerfiles" \
 ENV USER_ID=1000
 ENV GROUP_ID=1000
 
+VOLUME [ "/mnt" ]
+
 RUN apt-get update && apt-get upgrade -y && \
-    groupadd -g $GROUP_ID jekyll-dev && \
-    useradd -u $USER_ID -g $GROUP_ID -M -d /mnt -s /bin/false jekyll-dev
+    groupadd -g $GROUP_ID container-dev && \
+    useradd -u $USER_ID -g $GROUP_ID -M -d /mnt -s /bin/false container-dev
+
+USER container-dev
 
 CMD top -b

README.md

@@ -0,0 +1,4 @@
+# jekyll-dev
+
+Simple container to learn building Dockerfiles.
+