[arrays.dd] Improve pointer docs

Document dereference and address of operators.
Mention pointing to multiple elements and how this is not @safe.

Author: ntrel

spec/arrays.dd

@@ -18,13 +18,24 @@ $(H2 $(LNAME2 array-kinds, Kinds))
 
 $(H3 $(LNAME2 pointers, Pointers))
 
+        $(P A pointer to type $(D T) has a value which is a reference (address) to another
+        object of type $(D T). It is commonly called a $(I pointer to T) and it's type is
+        `T*`. To access the object value, use the `*` dereference operator:
+        )
+
+$(SPEC_RUNNABLE_EXAMPLE_RUN
 ---------
 int* p;
----------
 
-        $(P A pointer to type $(I T) has a value which is a reference (address) to another
-        object of type $(I T). It is commonly called a $(I pointer to T).
-        )
+assert(p == null);
+p = new int(5);
+assert(p != null);
+
+assert(*p == 5);
+(*p)++;
+assert(*p == 6);
+---------
+)
 
         $(P If a pointer contains a $(I null) value, it is not pointing to a valid object.)
 
@@ -43,12 +54,33 @@ int* p;
         to a valid object of type $(I T).)
         ))
 
-        $(BEST_PRACTICE These are simple pointers to data.
-        Pointers are provided for interfacing with C and for
+        $(P To set a pointer to point at an existing object, use the
+        `&` *address of* operator:
+
+$(SPEC_RUNNABLE_EXAMPLE_RUN
+---------
+int i = 2;
+int* p = &i;
+
+assert(p == &i);
+assert(*p == 2);
+*p = 4;
+assert(i == 4);
+---------
+)
+
+        $(P These are simple pointers to data.
+        A pointer can manipulate a block of multiple values. Accessing more
+        than one value cannot be
+        $(DDLINK spec/memory-safe-d, Memory-Safe-D-Spec, `@safe`) as it
+        requires $(RELATIVE_LINK2 pointer-arithmetic, pointer arithmetic).
+        This is supported for interfacing with C and for
         specialized systems work.
-        There is no length associated with it, and so there is no way for the
+        A pointer has no length associated with it, so there is no way for the
         compiler or runtime to do bounds checking, etc., on it.
-        Most conventional uses for pointers can be replaced with
+        )
+
+        $(BEST_PRACTICE Most conventional uses for pointers can be replaced with
         dynamic arrays, $(D out) and $(D ref) parameters,
         and reference types.
         )