doc: add overview for release process (#3377)

Add a clickable diagram that outlines the release process and
infrastructure for Node.js.

Author: richardlau

doc/release-overview.md

@@ -0,0 +1,79 @@
+# Overview of release process and infrastructure for Node.js
+
+This is an overview of how the release process for Node.js works and how it interacts with Build WG infrastructure.
+Clicking on most labels will take you to the relevant area of the build repository or other repository owned by the Node.js organization.
+
+```mermaid
+flowchart TD
+    subgraph user[Releaser]
+      start([<a href='https://github.com/nodejs/node/blob/main/doc/contributing/releases.md'>Start</a>])
+      prepareRelease(<a href='https://github.com/nodejs/node/blob/main/doc/contributing/releases.md#7-ensure-that-the-release-branch-is-stable'>Prepare the release</a>)
+      startTestBuilds(<a href='https://github.com/nodejs/node/blob/main/doc/contributing/releases.md#7-ensure-that-the-release-branch-is-stable'>Start test builds</a>)
+      readyToRelease{Ready for release?}
+      
+      startReleaseBuilds(<a href='https://github.com/nodejs/node/blob/main/doc/contributing/releases.md#9-produce-release-builds'>Start release build</a>)
+      promote(<a href='https://github.com/nodejs/node/blob/main/tools/release.sh'>Promote</a>)
+      blog(<a href='https://github.com/nodejs/nodejs.org/blob/main/scripts/release-post/index.mjs'>Create blog post</a>)
+      done([End])
+
+      start-->prepareRelease-->startTestBuilds-->readyToRelease
+      readyToRelease--No-->prepareRelease
+      readyToRelease--Yes-->startReleaseBuilds-->promote-->blog-->done
+    end
+    subgraph github[GitHub]
+      ghCode[<a href='https://github.com/nodejs/node'>nodejs/node</a>]
+      ghWebsite[<a href='https://github.com/nodejs/nodejs.org'>nodejs/nodejs.org</a>]
+      
+      %% This invisible link is to aid the layout of the flowchart, stacking the two repositories vertically
+      ghCode ~~~ ghWebsite
+    end
+    subgraph buildInfra[Infrastructure owned by Build WG]
+    subgraph ci[Test CI]
+      testBuilds(<a href='https://ci.nodejs.org/job/node-test-pull-request/'>Test builds</a>)
+    end
+    subgraph ci-release[Release CI]
+      releaseBuilds(<a href='https://ci-release.nodejs.org/job/iojs+release/'>Release builds</a>)
+    end
+    subgraph www[www server]
+      staging[(staging)]
+      promotion(<a href='https://github.com/nodejs/build/tree/main/ansible/www-standalone/tools/promote'>Promotion</a>)
+      dist[(dist)]
+      rebuildIdx(<a href='https://github.com/nodejs/nodejs-dist-indexer'>Rebuild index</a>)
+      rebuildWebsite(<a href='https://github.com/nodejs/build/blob/main/ansible/www-standalone/resources/scripts/build-site.sh'>Rebuild website</a>)
+      queueCDN[<a href='https://github.com/nodejs/build/blob/main/ansible/www-standalone/resources/scripts/queue-cdn-purge.sh'>Queue CDN purge</a>]
+      webhook(<a href='https://github.com/nodejs/build/blob/main/ansible/www-standalone/resources/config/github-webhook.json.j2'>Webhook</a>)
+
+      staging-->promotion-->dist-->rebuildIdx
+
+      subgraph chkIndex[Check index]
+        idxChanged{<a href='https://github.com/nodejs/build/blob/main/ansible/www-standalone/resources/scripts/check-build-site.sh'>Index Changed?</a>}
+
+        idxChanged--No-->idxChanged
+      end
+      
+      rebuildIdx-.->idxChanged
+      webhook-->rebuildWebsite
+      idxChanged--Yes-->rebuildWebsite
+      rebuildWebsite-->queueCDN-.->purgeQueued
+
+      subgraph cdn[CDN purge queue]
+        purgeQueued{<a href='https://github.com/nodejs/build/blob/main/ansible/www-standalone/resources/scripts/cdn-purge.sh.j2'>CDN purge queued?</a>}
+        purge(<a href='https://github.com/nodejs/build/blob/main/ansible/www-standalone/resources/scripts/cdn-purge.sh.j2'>CDN purge</a>)
+
+        purgeQueued--No-->purgeQueued
+        purgeQueued--Yes-->purge
+      end
+    end
+    end
+    prepareRelease-->|Open/update pull request|ghCode
+    startTestBuilds-->testBuilds
+    startReleaseBuilds-->releaseBuilds
+    ghWebsite-.->|Pull request merged|webhook
+    promote-->promotion
+    blog-->|Open pull request|ghWebsite
+    releaseBuilds-->staging
+    purge-->cloudflare
+
+    %% This invisible link is to aid the layout of the flowchart, stacking the "Test CI" subgraph above the "Release CI" subgraph
+    ci ~~~ ci-release
+```