Merge branch 'docs-aqualls-gitlab-metrics' into 'master'

Docs: tone and style, GitLab metrics page

See merge request gitlab-org/gitlab!33889

doc/.vale/gitlab/Acronyms.yml

@@ -40,6 +40,7 @@ exceptions:
   - POST
   - PUT
   - RSA
+  - RSS
   - SAML
   - SCP
   - SCSS
@@ -51,6 +52,7 @@ exceptions:
   - TIP
   - TLS
   - TODO
+  - UNIX
   - URI
   - URL
   - VPC

doc/.vale/gitlab/spelling-exceptions.txt

@@ -113,6 +113,7 @@ Dreamweaver
 Elasticsearch
 enablement
 enqueued
+ETag
 Excon
 expirable
 Facebook