Add document to install ebtables, ethtool (#4800)

* Add document to install ebtables, ethtool

* Fix markdown typo

* Fix typo , thanks tengqm

* Fix sentence

docs/setup/independent/install-kubeadm.md

@@ -52,6 +52,24 @@ The pod network plugin you use (see below) may also require certain ports to be
 open. Since this differs with each pod network plugin, please see the
 documentation for the plugins about what port(s) those need.
 
+## Installing ebtables ethtool
+
+If you see the following warnings while running `kubeadm init`
+
+```
+[preflight] WARNING: ebtables not found in system path                          
+[preflight] WARNING: ethtool not found in system path                           
+```
+
+Then you may be missing ebtables and ethtool on your Linux machine. You can install them with the following commands: 
+
+```
+# For ubuntu/debian users, try 
+apt install ebtables ethtool
+
+# For CentOS/Fedora users, try 
+yum install ebtables ethtool
+```
 
 ## Installing Docker