Update build instructions in CONTRIBUTING.md to match the new subdirectory layout (#435)
Update build instructions in CONTRIBUTING.md to match the new subdirectory layout (#435)

Signed-off-by: Brian Pane <5720439aa8fe33541c355982794f1a4cb6b27628@pinterest.com>
jrajahalme/envoy-api,jrajahalme/envoy-api,lyft/envoy-api,jrajahalme/envoy-api,lyft/envoy-api,jrajahalme/envoy-api,lyft/envoy-api