[docs] Add git submodules tips and FAQ

Change-Id: Ic20d801d5ec2310d7a2aaf0ca677fd6b00f201da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4778087
Reviewed-by: Erik Staab <[email protected]>
Commit-Queue: Josip Sokcevic <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1183433}
diff --git a/docs/README.md b/docs/README.md
index 1b5e3db..1114654b 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -100,6 +100,7 @@
 *   [Git Cookbook](git_cookbook.md) - A collection of git recipes for common
     tasks
 *   [Git Tips](git_tips.md) - More git tips
+*   [Git submodules](git_submodules.md) - Git submodule (tips, FAQ)
 
 ### Clang
 *   [Clang Compiler](clang.md) - General information on the clang compiler, used