add explanation to cloud build section docs
Add explanation to google cloud build section docs to make clear the
differences between the gcloud command and the skaffold build process with GCB.
This  fixes
@@ -71,6 +71,13 @@ with it. After Cloud Build finishes building your artifacts, they will
be saved to the specified remote registry, such as
[Google Container Registry](https://cloud.google.com/container-registry/).
+Skaffold Google Cloud Build process differs from the gcloud command
+`gcloud builds submit`. Skaffold will create a list of dependent files
+and submit a tar file to GCB. It will then generate a single step `cloudbuild.yaml`
+and will start the building process. Skaffold does not honors `.gitignore` or `.gcloudignore`
+exclusions. If you need to ignore files use `.dockerignore`. Any `cloudbuild.yaml` found will not
+be used in the build process.
+
### Configuration
To use Cloud Build, add build type `googleCloudBuild` to the `build`
