docs: add FAQ regarding GOROOT env var (#3122)

Co-authored-by: Camila Macedo <[email protected]>

Author: demonCoder95

website/content/en/docs/faq.md

@@ -123,10 +123,30 @@ func (r *ReconcileMemcached) Reconcile(request reconcile.Request) (reconcile.Res
 	}
 ```
 
+## I see deepcopy errors and image build fails. How do I fix this?
+
+When you run the ```operator-sdk generate k8s``` command, you might see an error like this
+
+```
+INFO[0000] Running deepcopy code-generation for Custom Resource group versions: [cache:[v1alpha1], ] 
+F0523 01:18:27.122034    5157 deepcopy.go:885] Hit an unsupported type invalid type for invalid type, from github.com/example-inc/memcached-operator/pkg/apis/cache/v1alpha1.Memcached
+```
+
+This is because of the `GOROOT` environment variable not being set. More details [here][goroot-github-issue].
+
+In order to fix this, you simply need to export the `GOROOT` environment variable
+
+```
+$ export GOROOT=$(go env GOROOT)
+```
+
+This will work for the current environment. To persist this fix, add the above line to your environment's config file, ex. `bashrc` file.
+
 [kube-apiserver_options]: https://kubernetes.io/docs/reference/command-line-tools-reference/kube-apiserver/#options
 [controller-runtime_faq]: https://github.com/kubernetes-sigs/controller-runtime/blob/master/FAQ.md#q-how-do-i-have-different-logic-in-my-reconciler-for-different-types-of-events-eg-create-update-delete
 [finalizer]: /docs/golang/quickstart/#handle-cleanup-on-deletion
 [gc-metrics]:/docs/golang/monitoring/prometheus/#garbage-collection
 [cr-faq]:https://github.com/kubernetes-sigs/controller-runtime/blob/master/FAQ.md
 [client.Reader]:https://godoc.org/sigs.k8s.io/controller-runtime/pkg/client#Reader
 [rbac]:https://kubernetes.io/docs/reference/access-authn-authz/rbac/
+[goroot-github-issue]:https://github.com/operator-framework/operator-sdk/issues/1854#issuecomment-525132306