doc/user-guide.md: update Go modules support section (#1663)

Author: Eric Stroczynski

doc/user-guide.md

@@ -43,14 +43,6 @@ If using Go modules (the default dependency manager) in your project, ensure you
 > - Invoke the go command in a directory outside of the $GOPATH/src tree, with a valid go.mod file in the current directory or any parent of it and the environment variable GO111MODULE unset (or explicitly set to auto).
 > - Invoke the go command with GO111MODULE=on environment variable set.
 
-As of now, the SDK only supports initializing new projects in `$GOPATH/src`. We intend to support all go module modes for projects in the near future.
-
-You can set `GO111MODULE` in your CLI to activate currently supported behavior by running the following command:
-
-```sh
-$ export GO111MODULE=on
-```
-
 ##### Vendoring
 
 By default, an operator's dependencies are managed with `modules` and `--vendor=false`, so calls to `go {build,clean,get,install,list,run,test}` by `operator-sdk` subcommands will use an external modules directory. Execute `go help modules` for more information.
@@ -204,10 +196,18 @@ Once this is done, there are two ways to run the operator:
 
 **Note**: `operator-sdk build` invokes `docker build` by default, and optionally `buildah bud`. If using `buildah`, skip to the `operator-sdk build` invocation instructions below. If using `docker`, make sure your docker daemon is running and that you can run the docker client without sudo. You can check if this is the case by running `docker version`, which should complete without errors. Follow instructions for your OS/distribution on how to start the docker daemon and configure your access permissions, if needed.
 
-**Note**: If using Go modules and a `vendor/` directory, run
+**Note**: If a `go.mod` file and a `vendor/` directory are present, run
+
 ```sh
 $ go mod vendor
 ```
+
+or if a `Gopkg.toml` file is present run
+
+```sh
+$ dep ensure
+```
+
 before building the memcached-operator image.
 
 Build the memcached-operator image and push it to a registry:
@@ -413,7 +413,7 @@ func main() {
 
 **NOTES:**
 
-* After adding new import paths to your operator project, run `go mod vendor` if using modules and a `vendor/` directory (or `dep ensure` if you set `--dep-manager=dep` when initializing your project) in the root of your project directory to fulfill these dependencies.
+* After adding new import paths to your operator project, run `go mod vendor` if a `go.mod` file and a `vendor/` directory are present (or `dep ensure` if a `Gopkg.toml` file is present) in the root of your project directory to fulfill these dependencies.
 * Your 3rd party resource needs to be added before add the controller in `"Setup all Controllers"`.
 
 ### Handle Cleanup on Deletion
@@ -488,7 +488,7 @@ func (r *ReconcileMemcached) Reconcile(request reconcile.Request) (reconcile.Res
 func (r *ReconcileMemcached) finalizeMemcached(reqLogger logr.Logger, m *cachev1alpha1.Memcached) error {
 	// TODO(user): Add the cleanup steps that the operator
 	// needs to do before the CR can be deleted. Examples
-	// of finalizers include performing backups and deleting 
+	// of finalizers include performing backups and deleting
 	// resources that are not owned by this CR, like a PVC.
 	reqLogger.Info("Successfully finalized memcached")
 	return nil