Add guide: Rename default branch to main

Author: eliot-akira

docs/pages/guides/main-branch.md

@@ -0,0 +1,17 @@
+# Rename default branch to `main`
+
+The standard default branch name is `main` for all projects. Follow the steps below to update older projects using `master` branch.
+
+It can be done in the GitHub repository, under Settings -> Default branch.
+
+- https://github.com/TangibleInc/example-plugin/settings
+
+After the switch, it also requires a change in any locally cloned repo. 
+
+```sh
+git checkout master
+git branch -m master main
+git fetch origin
+git branch --unset-upstream
+git branch -u origin/main
+```

docs/pages/guides/plugin-upgrade.md

@@ -47,6 +47,8 @@ Rename main branch from "master" to "main".
 git branch -M main
 ```
 
+For existing projects, see the guide [Rename default branch to `main`](main-branch).
+
 Push to remote `origin`, setting it as the upstream of main branch.
 
 ```sh

docs/sidebars.ts

@@ -145,6 +145,10 @@ const sidebars: SidebarsConfig = {
           type: 'doc',
           id: 'guides/plugin-upgrade',
         },
+        {
+          type: 'doc',
+          id: 'guides/main-branch',
+        },
         {
           type: 'doc',
           id: 'guides/github-pages',