checkupdates: add page (#7774)

pages/linux/checkupdates.md

@@ -0,0 +1,20 @@
+# checkupdates
+
+> Tool to check pending updates in Arch Linux.
+> More information: <https://man.archlinux.org/man/checkupdates.8>.
+
+- List pending updates:
+
+`checkupdates`
+
+- List pending updates and download the packages to the pacman cache:
+
+`checkupdates --download`
+
+- List pending updates using a specific pacman database:
+
+`CHECKUPDATES_DB={{path/to/directory}} checkupdates`
+
+- Display help:
+
+`checkupdates --help`