Improvements in the documentation (README.md) (#3907)

* Added suggestions by @yongtang

Signed-off-by: Chanakya-Ekbote <ca10@iitbbs.ac.in>

* Removed trailing whitespaces

Signed-off-by: Chanakya-Ekbote <ca10@iitbbs.ac.in>

README.md

@@ -87,15 +87,38 @@ CoreDNS-1.6.6
 linux/amd64, go1.13.5, aa8c32
 ~~~
 
+The following could be used to query the CoreDNS server that is running now:
+
+~~~ txt
+dig @127.0.0.1 -p 53 www.example.com
+~~~
+
 Any query sent to port 53 should return some information; your sending address, port and protocol
 used. The query should also be logged to standard output.
 
+The configuration of CoreDNS is done through a file named `Corefile`. When CoreDNS starts, it will
+look for the `Corefile` from the current working directory. A `Corefile` for CoreDNS server that listens
+on port `53` and enables `whoami` plugin is:
+
+~~~ corefile
+.:53 {
+    whoami
+}
+~~~
+
+Sometimes port number 53 is occupied by system processes. In that case you can start the CoreDNS server
+while modifying the Corefile as given below so that the CoreDNS server starts on port 1053.
+
+~~~ corefile
+.:1053 {
+    whoami
+}
+~~~
+
 If you have a Corefile without a port number specified it will, by default, use port 53, but you can
 override the port with the `-dns.port` flag: `coredns -dns.port 1053`, runs the server on port 1053.
 
-Start a simple proxy. You'll need to be root to start listening on port 53.
+A Corefile for a CoreDNS server that forward any queries to an upstream DNS (e.g., `8.8.8.8`) is as follows:
-
-`Corefile` contains:
 
 ~~~ corefile
 .:53 {