Add pacman command alternative for

linux/arch/README.md

@@ -6,4 +6,17 @@
 
 ```
 pacman -Rcns <package>
-```
+```
+
+### See which package provides which file
+
+Search for a full filename
+```
+pacman -F $filename
+```
+
+Search for a regex
+
+```
+pacman -Fx $expr
+```