Update BFS_design.md
Update BFS_design.md

baidu/bfs,yvxiang/coverage_for_bfs,yvxiang/coverage_for_bfs,linyvxiang/dfs,lylei/dfs,lylei/dfs,myawan/bfs-1,lylei/dfs,bluebore/dfs,myawan/bfs-1,lylei/dfs,baidu/bfs,linyvxiang/dfs,bluebore/bfs,bluebore/bfs,yvxiang/coverage_for_bfs,baidu/bfs,yvxiang/coverage_for_bfs,00k/ToyDFS,00k/ToyDFS,baidu/bfs,myawan/bfs-1,bluebore/bfs,bluebore/dfs,bluebore/dfs,yvxiang/dfs,yvxiang/dfs,linyvxiang/dfs,myawan/bfs-1,yvxiang/dfs,yvxiang/dfs