chore: import upstream snapshot with attribution

docs/en/dummy_server.md

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+If your program only uses client in brpc or doesn't use brpc at all, but you also want to use built-in services in brpc. The thing you should do is to start an empty server, which is called **dummy server**.
+
+# client in brpc is used
+
+Create a file named dummy_server.port which contains a port number(such as 8888) in the running directory of program, a dummy server would be started at this port. All of the bvar in the same process can be seen by visiting its built-in service.
+![img](../images/dummy_server_1.png) ![img](../images/dummy_server_2.png) 
+
+![img](../images/dummy_server_3.png)
+
+# brpc is not used at all
+
+You must manually add the dummy server. First read [Getting Started](getting_started.md) to learn how to download and compile brpc, and then add the following code snippet at the program entry:
+
+```c++
+#include <brpc/server.h>
+ 
+...
+ 
+int main() {
+    ...
+    brpc::StartDummyServerAt(8888/*port*/);
+    ...
+}
+```