provider/profitbricks Doc update (hashicorp#11643)

* Terraform ProfitBricks Builder

* make fmt

* Merge remote-tracking branch 'upstream/master' into terraform-provider-profitbricks

# Conflicts:
#	command/internal_plugin_list.go

* Addressing PR remarks

* Removed importers

* Added ProfitBricks Data Sources

* Added documentation

* Updated to REST v3:
- nat parameter for Nics
- availabilityZone for Volumes

Minor code clean up

* Minor code clean up

* Fixed typo in volume documentation

* make fmt

* Addressing requested changes

* Added a step in load balancer tests in CheckDestroy where we are making sure that the test doesn't leave dangling resources in ProfitBricks

* Changed expected image name

* Fixed data center test
Code clean up

* Added missing parameter to ProfitBricks provider docs.

Author: Jasmin Gacic

website/source/docs/providers/profitbricks/index.html.markdown

@@ -21,6 +21,7 @@ The provider needs to be configured with proper credentials before it can be use
 ```
 $ export PROFITBRICKS_USERNAME="profitbricks_username" 
 $ export PROFITBRICKS_PASSWORD="profitbricks_password"
+$ export PROFITBRICKS_API_URL="profitbricks_rest_url"
 ```
 
 Or you can provide your credentials like this:
@@ -35,6 +36,7 @@ The credentials provided in `.tf` file will override credentials in the environm
 provider "profitbricks" {
     username = "profitbricks_username"
     password = "profitbricks_password"
+    endpoint = "profitbricks_rest_url"
     retries = 100
 }
 
@@ -53,6 +55,8 @@ The following arguments are supported:
 
 * `password` - (Required) If omitted, the `PROFITBRICKS_PASSWORD` environment variable is used.
 
+* `endpoint` - (Required) If omitted, the `PROFITBRICKS_API_URL` environment variable is used.
+
 * `retries` - (Optional) Number of retries while waiting for a resource to be provisioned. Default value is 50.