Worker concepts doc (#3487)

* Worker concepts doc

* Apply suggestions from code review

* Apply suggestions from code review

Co-authored-by: Dan Heath <76443935+Dan-Heath@users.noreply.github.com>
Co-authored-by: Irena Rindos <irenarindos@users.noreply.github.com>

* Apply suggestions from code review

* Update website/content/docs/concepts/workers.mdx

* docs: Minor copy edits, clean up Markdown

* doc: Omit parentheses

---------

Co-authored-by: Dan Heath <76443935+Dan-Heath@users.noreply.github.com>
Co-authored-by: Irena Rindos <irenarindos@users.noreply.github.com>

website/data/docs-nav-data.json

@@ -132,6 +132,10 @@
         "title": "Overview",
         "path": "concepts"
       },
+      {
+        "title": "Workers",
+        "path": "concepts/workers"
+      },
       {
         "title": "Identity and access management",
         "path": "concepts/iam"