Merge pull request #3093 from m-Bilal/fix-kubernetes-source-location-doc

docs: add example to specify kubernetes source location

Author: k8s-ci-robot

site/content/docs/user/quick-start.md

@@ -260,6 +260,11 @@ Currently, kind supports one default way to build a `node-image`
 if you have the [Kubernetes][kubernetes] source in your host machine
 (`$GOPATH/src/k8s.io/kubernetes`), by using `docker`.
 
+You can also specify a different path to kubernetes source using 
+```
+kind build node-image /path/to/kubernetes/source
+```
+
 > **NOTE**: Building Kubernetes node-images requires everything building upstream
 > Kubernetes requires, we wrap the upstream build. This includes Docker with buildx.
 > See: https://git.k8s.io/community/contributors/devel/development.md#building-kubernetes-with-docker