update build.txt to add submodule part
tree773f99b82f8282379b8de1d5b96c732ad8bfb313
-rw-r--r-- 388 .gitignore
-rw-r--r-- 391 .gitmodules
drwxr-xr-x - Languages
-rw-r--r-- 3582 build.txt
drwxr-xr-x - common
drwxr-xr-x - contrib
drwxr-xr-x - doc
drwxr-xr-x - ext
drwxr-xr-x - src
drwxr-xr-x - test