Update URLs in docs; replace some uses of 'master'

Bug: 1231155
Change-Id: I0634229c0739c97ac0d7530dd58c33771958149a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3042058
Reviewed-by: Toby Huang <[email protected]>
Commit-Queue: Andrew Williams <[email protected]>
Cr-Commit-Position: refs/heads/master@{#903745}
diff --git a/docs/ios/build_instructions.md b/docs/ios/build_instructions.md
index 09e356b..705e101 100644
--- a/docs/ios/build_instructions.md
+++ b/docs/ios/build_instructions.md
@@ -318,7 +318,7 @@
 
 The first command updates the primary Chromium source repository and rebases
 any of your local branches on top of tip-of-tree (aka the Git branch
-`origin/master`). If you don't want to use this script, you can also just use
+`origin/main`). If you don't want to use this script, you can also just use
 `git pull` or other common Git commands to update the repo.
 
 The second command syncs dependencies to the appropriate versions and re-runs