Replace `pacman -Sy` with `pacman -S` in Arch Linux installation guides (#252)

According to ArchWiki, using `pacman -Sy` to perform partial upgrades
is not supported.

docs/guide/quick-start.md

@@ -85,8 +85,8 @@ brew install xmake
 
 ::: code-group
 
-```sh [Archlinux]
-sudo pacman -Sy xmake
+```sh [Arch Linux]
+sudo pacman -S xmake
 ```
 
 ```sh [Alpine]

docs/zh/guide/quick-start.md

@@ -87,8 +87,8 @@ brew install xmake
 
 ::: code-group
 
-```sh [Archlinux]
-sudo pacman -Sy xmake
+```sh [Arch Linux]
+sudo pacman -S xmake
 ```
 
 ```sh [Alpine]