Add information about build

README.md

@@ -8,6 +8,11 @@ The System Settings application for Cutefish Desktop.
 sudo pacman -S extra-cmake-modules qt5-base qt5-quickcontrols2 freetype2 fontconfig networkmanager-qt modemmanager-qt kcoreaddons
 ```
 
+For Ubuntu, to meet the demand of module `icu-i18n`, you need to:
+```shell
+sudo apt install libicu-dev
+```
+
 ## Build
 
 ```shell
@@ -15,6 +20,7 @@ mkdir build
 cd build
 cmake ..
 make
+sudo make install
 ```
 
 ## Install