README.md: Update the way we build the application

Signed-off-by: Sergiu Moga <sergiu.moga@protonmail.com>
Reviewed-by: Gabriel Mocanu <gabi.mocanu98@gmail.com>
Approved-by: Razvan Deaconescu <razvan.deaconescu@cs.pub.ro>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Pull-Request: unikraft#3

Author: mogasergiu

README.md

@@ -1,10 +1,49 @@
 # Unikraft "hello world" Application
 
-To build and run this application please use the `kraft` script:
+This application prints a basic "Hello World!" message.
 
-    pip3 install git+https://github.com/unikraft/kraft.git
-    mkdir my-first-unikernel && cd my-first-unikernel
-    kraft up -p PLATFORM -m ARCHITECTURE helloworld
+To configure, build and run the application you need to have [kraft](https://github.com/unikraft/kraft) installed.
+
+To be able to run it, configure the application to run on the desired platform and architecture:
+```
+$ kraft configure -p PLATFORM -m ARCH
+```
+
+Build the application:
+```
+$ kraft build
+```
+
+And, finally, run the application:
+```
+$ kraft run
+Hello World!
+```
+
+If you want to have more control you can also configure, build and run the application manually.
+
+To configure it with the desired features:
+```
+$ make menuconfig
+```
+
+Build the application:
+```
+$ make
+```
+
+Run the application:
+- If you built the application for `kvm`:
+```
+sudo qemu-system-x86_64 -kernel "build/app-helloworld_kvm-x86_64" \
+                        -enable-kvm \
+                        -nographic
+```
+
+- If you built the application for `linuxu`:
+```
+./build/app-helloworld_linuxu-x86_64
+```
 
 For more information about `kraft` type ```kraft -h``` or read the
 [documentation](http://docs.unikraft.org).