update opm dockerfile example to cache (operator-framework#1033)

Signed-off-by: Jordan Keister <[email protected]>

Signed-off-by: Jordan Keister <[email protected]>

Author: grokspawn

opm-example.Dockerfile

@@ -4,10 +4,11 @@ FROM quay.io/operator-framework/opm:latest
 
 # Configure the entrypoint and command
 ENTRYPOINT ["/bin/opm"]
-CMD ["serve", "/configs"]
+CMD ["serve", "/configs", "--cache-dir=/tmp/cache"]
 
-# Copy declarative config root into image at /configs
+# Copy declarative config root into image at /configs and pre-populate serve cache
 ADD index /configs
+RUN ["/bin/opm", "serve", "/configs", "--cache-dir=/tmp/cache", "--cache-only"]
 
 # Set DC-specific label for the location of the DC root directory
 # in the image