Update source_install-nebula-graph-by-rpm-or-deb.md (#748)

added dpkg/rpm examples

some users queried this in wechat/slack on what is the package_name

docs-2.0/reuse/source_install-nebula-graph-by-rpm-or-deb.md

@@ -121,12 +121,25 @@ Prepare the right [resources](https://docs.nebula-graph.io/{{nebula.release}}/4.
     sudo rpm -ivh --prefix=<installation_path> <package_name>
     ```
 
+    For example, install the downloaded {{ nebula.release }} `CentOS 7` package: 
+
+    ```bash
+    sudo rpm -ivh nebula-graph-{{ nebula.release }}.el7.x86_64.rpm
+    ```
+
 * Use the following syntax to install with a DEB package.
 
     ```bash
     sudo dpkg -i --instdir==<installation_path> <package_name>
     ```
 
+    For example, install the downloaded {{ nebula.release }} `Ubuntu 18.04` package: 
+
+    ```bash
+    sudo dpkg -i nebula-graph-{{ nebula.release }}.ubuntu1804.amd64.deb
+    ```
+
+
   !!! note
 
         The default installation path is `/usr/local/nebula/`.