Merge pull request #4617 from cyk2018/patch-1

[Doc]Update user_manual.md for static linker

Author: martin-frbg

docs/user_manual.md

@@ -159,7 +159,7 @@ int main(int argc, char* argv[])
 ```
 
 ```
-gcc -o time_dgemm time_dgemm.c /your/path/libopenblas.a
+gcc -o time_dgemm time_dgemm.c /your/path/libopenblas.a -lpthread
 ./time_dgemm <m> <n> <k>
 ```