Fix gitlab documentation (#14803)

* fix gitlab_project resource documentation

* improve gitlab provider documentation

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

@@ -37,5 +37,6 @@ The following arguments are supported in the `provider` block:
   it can also be sourced from the `GITLAB_TOKEN` environment variable.
 
 * `base_url` - (Optional) This is the target GitLab base API endpoint. Providing a value is a
-  requirement when working with GitLab CE or GitLab Enterprise.  It is optional to provide this value and
-  it can also be sourced from the `GITLAB_BASE_URL` environment variable.  The value must end with a slash.
+  requirement when working with GitLab CE or GitLab Enterprise e.g. https://my.gitlab.server/api/v3/.
+  It is optional to provide this value and it can also be sourced from the `GITLAB_BASE_URL` environment variable.
+  The value must end with a slash.

website/source/docs/providers/gitlab/r/project.html.markdown

@@ -41,7 +41,7 @@ The following arguments are supported:
 
 * `snippets_enabled` - (Optional) Enable snippets for the project.
 
-* `visbility_level` - (Optional) Set to `public` to create a public project.
+* `visibility_level` - (Optional) Set to `public` to create a public project.
   Valid values are `private`, `internal`, `public`.
   Repositories are created as private by default.