chore: document first-level submodule checkout

README.md

@@ -7,15 +7,20 @@ repository commits that make up a working checkout.
 ## Clone
 
 ```bash
-git clone --recurse-submodules ssh://git@gitea.bowong.cc:222/comi-logic/cfw-workspace.git
+git clone ssh://git@gitea.bowong.cc:222/comi-logic/cfw-workspace.git
+cd cfw-workspace
+git submodule update --init
 ```
 
 For an existing clone:
 
 ```bash
-git submodule update --init --recursive
+git submodule update --init
 ```
 
+Do not use `--recursive` by default. Some child repositories have their own
+historical nested submodules that are not required for opening this workspace.
+
 ## Subprojects
 
 | Path | Repository | Notes |