docs: clarify where .jekyll-metadata comes from (#8646)

Merge pull request 8646

docs/_data/config_options/build.yml

@@ -84,10 +84,11 @@
 
 - name: Incremental build
   description: >-
-    Enable the experimental incremental build feature. Incremental build only
+    Enable the experimental
-    re-builds posts and pages that have changed, resulting in significant performance
+    <a href="/docs/configuration/incremental-regeneration/">incremental
-    improvements for large sites, but may also break site generation in certain
+    build</a> feature. Incremental build only re-builds posts and pages that
-    cases.
+    have changed, resulting in significant performance improvements for large
+    sites, but may also break site generation in certain cases.
   option: "incremental: BOOL"
   flag: -I, --incremental
 

docs/_docs/structure.md

@@ -188,9 +188,11 @@ An overview of what each of these does:
         <p>
           This helps Jekyll keep track of which files have not been modified
           since the site was last built, and which files will need to be
-          regenerated on the next build. This file will not be included in the
+          regenerated on the next build. Only created when using
-          generated site. It’s probably a good idea to add this to your
+          <a href="/docs/configuration/incremental-regeneration/">
-          <code>.gitignore</code> file.
+          incremental regeneration</a> (e.g.: with <code>jekyll serve -I</code>).
+          This file will not be included in the generated site. It’s probably
+          a good idea to add this to your <code>.gitignore</code> file.
         </p>
       </td>
     </tr>