Update README.md

README.md

@@ -117,7 +117,12 @@
 - Apple OSX(Darwin), both 32 and 64bits.
 - All hardware with x86/x86_64/arm/mips cpu.
 - Windows.
-- **You must use git to clone the complete code. Do not download the source code by downloading zip package. Otherwise, the sub-module code will not be downloaded by default.**
+- **You must use git to clone the complete code. Do not download the source code by downloading zip package. Otherwise, the sub-module code will not be downloaded by default.You can do it like this:**
+```
+git clone https://github.com/zlmediakit/ZLMediaKit.git
+cd ZLMediaKit
+git submodule update --init
+```