Update README.Linux.md

I did not have build-essential installed and ran into some errors on the make step. Might be good just to remind people that they need the basic build tools installed.

Author: alexmarchant

README.Linux.md

@@ -31,6 +31,9 @@ Compile latest V8
 
 
 ```
+# Install `build-essential` if you haven't already:
+sudo apt-get install build-essential
+
 # Install `libicu-dev` if you haven't already:
 sudo apt-get install libicu-dev