Update object comprehensions docs

- Add example with a do...while loop
- Fix colon in an existing example

civet.dev/reference.md

@@ -1940,7 +1940,7 @@ max := for max item of array
 ### Object Comprehensions
 
 Loops can also accumulate their body values into an object.
-When any loop is found is found within an object expression,
+When any loop is found is found within a braced object expression,
 its body value is spread into the containing object.
 
 <Playground>
@@ -1951,13 +1951,22 @@ doubled := {
 }
 </Playground>
 
+<Playground>
+i .= 1
+squares := {
+  do
+    [i]: i * i
+  while i++ < 10
+}
+</Playground>
+
 The loop can exist anywhere a property is expected.
 It can be freely mixed with other object properties.
 
 <Playground>
 rateLimits := {
   admin: Infinity,
-  for user of users:
+  for user of users
     [user.name]: getRemainingLimit(user)
 }
 </Playground>