Node exporter: tone and style updates

Tone, style, and word choice updates. Remove outdated info.

doc/.vale/gitlab/Acronyms.yml

@@ -15,6 +15,7 @@ exceptions:
   - ASCII
   - AWS
   - CNAME
+  - CPU
   - CSS
   - CSV
   - DNS

doc/administration/monitoring/prometheus/node_exporter.md

@@ -6,27 +6,24 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Node exporter
 
->**Note:**
-Available since Omnibus GitLab 8.16. For installations from source you'll
-have to install and configure it yourself.
-
-The [node exporter](https://github.com/prometheus/node_exporter) allows you to measure
+The [node exporter](https://github.com/prometheus/node_exporter) enables you to measure
 various machine resources such as memory, disk and CPU utilization.
 
+NOTE: **Note:**
+For installations from source you'll have to install and configure it yourself.
+
 To enable the node exporter:
 
-1. [Enable Prometheus](index.md#configuring-prometheus)
-1. Edit `/etc/gitlab/gitlab.rb`
-1. Add or find and uncomment the following line, making sure it's set to `true`:
+1. [Enable Prometheus](index.md#configuring-prometheus).
+1. Edit `/etc/gitlab/gitlab.rb`.
+1. Add (or find and uncomment) the following line, making sure it's set to `true`:
 
    ```ruby
    node_exporter['enable'] = true
    ```
 
-1. Save the file and [reconfigure GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure)
-   for the changes to take effect
-
-Prometheus will now automatically begin collecting performance data from
-the node exporter exposed under `localhost:9100`.
+1. Save the file, and [reconfigure GitLab](../../restart_gitlab.md#omnibus-gitlab-reconfigure)
+   for the changes to take effect.
 
-[← Back to the main Prometheus page](index.md)
+Prometheus will now begin collecting performance data from the node exporter
+exposed at `localhost:9100`.