add installation instructions of Ubuntu

README.md

@@ -77,10 +77,9 @@ Finally, let's build xrdp source / sink modules. You'll have two .so files
 
 Some build tools and package development tools are required. Make sure install
 the tools.
-i```
+    
     sudo -s
     apt install build-essential dpkg-dev xrdp-pulseaudio-installer
-```
 
 ### Prepare & build