Update references to master branch

Change-Id: I1bfd1b655af6cdfbd64452b1e594a276425095fe
Bug: skia:11987
Docs-Preview: https://skia.org/?cl=410790
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/410790
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
diff --git a/site/docs/dev/contrib/submit.md b/site/docs/dev/contrib/submit.md
index d9ebcf0..bebb946 100644
--- a/site/docs/dev/contrib/submit.md
+++ b/site/docs/dev/contrib/submit.md
@@ -17,7 +17,7 @@
 <!--?prettify lang=sh?-->
 
     git config branch.autosetuprebase always
-    git checkout -b my_feature origin/master
+    git checkout -b my_feature origin/main
 
 After making your changes, create a commit
 
@@ -169,7 +169,7 @@
 Once your commit has gone in, you should delete the branch containing your
 change:
 
-    git checkout -q origin/master
+    git checkout -q origin/main
     git branch -D my_feature
 
 ## Final Testing