update README with example and info

README.md

@@ -3,14 +3,27 @@
 Container to run logspout + rsyslog and ingest docker logs and write them to
 disk as json.
 
+# Use Case
+
+I have a single box that runs a bunch of containers, and I want to log all
+those containers to datestamped logfiles as json.
+
+All of the other ways of commonly doing this involve 47 moving parts, so I
+made this container.  It uses logspout to ingest, and feeds into an rsyslog
+in the same container, which then writes them to disk as json.
+
+Figuring out how to use them is another matter; at least now they're saved
+in a way that is easy to tarball up and compress and scp somewhere else on a
+daily cronjob.
+
 # example
 
 ```
 docker \
     run \
     -d \
-    --restart-policy=unless-stopped \
+    --restart always \
-    -v /srv/z/logarchive:/var/logs \
+    -v /srv/z/archive/logs/current:/var/logs \
-    -v /var/run/docker.sock:/var/run.docker.sock \
+    -v /var/run/docker.sock:/var/run/docker.sock \
-    sneak/logwriter
+    sneak/logwriter@sha256:3229118cd23470206ffa0c1de37762ae9d5113e2720bdcf2c8576b5635763893
 ```