Fix line breaks and wording

Hard wrap lines, and perform some smaller changes. Done in a
separate commit to make rebasing / merging easier.

doc/user/project/clusters/index.md

@@ -275,25 +275,38 @@ If your cluster was created before GitLab 12.2, default `KUBE_NAMESPACE` will be
 
 The Kubernetes integration provides a `KUBECONFIG` with an auto-generated namespace
 to deployment jobs. It defaults to using project-environment specific namespaces
-of the form `<prefix>-<environment>`, where `<prefix>` is of the form `<project_name>-<project_id>` (see [Deployment
-variables](#deployment-variables)).
-
-The deployment namespace can be customized in a few ways:
-
-- You can choose between a **namespace per [environment](../../../ci/environments/index.md)** or a **namespace per project**. A namespace per environment is the default and recommended setting, as it prevents the mixing of resources between production and non-production environments.
-- When using a project-level cluster, you can additionally customize the namespace prefix. When using namespace-per-environment, the deployment namespace is `<prefix>-<environment>`, but otherwise just `<prefix>`.
-- For **non-managed** clusters, the auto-generated namespace is set in the `KUBECONFIG`, but the user is responsible for ensuring its existence. The value can be fully customized using [`environment:kubernetes:namespace`](../../../ci/environments/index.md#configuring-kubernetes-deployments)
-in `.gitlab-ci.yml`.
+of the form `<prefix>-<environment>`, where `<prefix>` is of the form
+`<project_name>-<project_id>`. To learn more, read [Deployment variables](#deployment-variables).
+
+You can customize the deployment namespace in a few ways:
+
+- You can choose between a **namespace per [environment](../../../ci/environments/index.md)**
+  or a **namespace per project**. A namespace per environment is the default and recommended
+  setting, as it prevents the mixing of resources between production and non-production environments.
+- When using a project-level cluster, you can additionally customize the namespace prefix.
+  When using namespace-per-environment, the deployment namespace is `<prefix>-<environment>`,
+  but otherwise just `<prefix>`.
+- For **non-managed** clusters, the auto-generated namespace is set in the `KUBECONFIG`,
+  but the user is responsible for ensuring its existence. You can fully customize
+  this value using
+  [`environment:kubernetes:namespace`](../../../ci/environments/index.md#configuring-kubernetes-deployments)
+  in `.gitlab-ci.yml`.
 
 NOTE: **Note:**
-When you customize the namespace, existing environments remain linked to their current namespaces until you [clear the cluster cache](#clearing-the-cluster-cache).
+When you customize the namespace, existing environments remain linked to their current
+namespaces until you [clear the cluster cache](#clearing-the-cluster-cache).
 
 CAUTION: **Warning:**
-By default, anyone who can create a deployment job can access any CI variable within an environment's deployment job. This includes `KUBECONFIG`, which gives access to any secret available to the associated service account in your cluster.
-To keep your production credentials safe, consider using [Protected Environments](../../../ci/environments/protected_environments.md), combined with either
+By default, anyone who can create a deployment job can access any CI variable within
+an environment's deployment job. This includes `KUBECONFIG`, which gives access to
+any secret available to the associated service account in your cluster.
+To keep your production credentials safe, consider using
+[Protected Environments](../../../ci/environments/protected_environments.md),
+combined with either
 
 - a GitLab-managed cluster and namespace per environment,
-- *or*, an environment-scoped cluster per protected environment (the same cluster can be added multiple times with multiple restricted service accounts).
+- *or*, an environment-scoped cluster per protected environment. The same cluster
+  can be added multiple times with multiple restricted service accounts.
 
 ### Integrations