docs: add more documentation to each of the modules in vlib (#13043)

vlib/arrays/README.md

@@ -1,4 +1,16 @@
 ## Description:
 
-`arrays` provides some generic functions for processing arrays.
+`arrays` is a module that provides utility functions to make working with arrays easier.
 
+## Examples:
+
+```v
+import arrays
+
+fn main() {
+	a := [1, 5, 7, 0, 9]
+	assert arrays.min(a) ? == 0
+	assert arrays.max(a) ? == 9
+	assert arrays.idx_min(a) ? == 3
+}
+```