README: update Docker information

Signed-off-by: Sean Cross <sean@xobs.io>

README.md

@@ -8,6 +8,12 @@ Install dependent packages with npm:
 npm i
 ```
 
+Or build a Docker image:
+
+```
+docker build -t reveal-serve .
+```
+
 ## Usage
 
 Run on your server.  Specify a secret with the `s` option.  Create a webhook that fires on the "push" event.
@@ -23,3 +29,17 @@ There are some environment variables that can be used to configure the server:
 * *RV_LISTEN_PORT*: The port number to listen to. Defaults to `9119`.
 * *RV_LISTEN_ADDR*: The local address to listen to.  Defaults to `0.0.0.0`
 * *RV_ROOT*: The root where all repos will go to.
+
+An example invocation would be:
+
+```
+docker run \
+    -d \
+    --restart unless-stopped \
+    --log-opt max-size=10m \
+    --name=reveal-serve \
+    -p 9119:80 \
+    -e RV_PREFIXES=https://github.com/example \
+    -e RV_SECRET=rvsecretkey \
+    reveal-serve
+```