improve readme

README.md

@@ -188,6 +188,7 @@ The different ways to specify a value can be grouped as "reads" and "writes":
 
 Objects (`@reg`, `@sym`) can be read or written as if they were a register, but only if the referenced object supports it.
 Other objects may produce a runtime fault or set the INVALID flag. 
+The object syntax is also used to read values yielded by a generator-like coroutine.
 
 In the instruction lists below, I will use the symbols `Rd` for reads, `Wr` for writes, `RW` for read-writes, and `@Obj` for object handles,
 with optional description after an apostrophe, such as: `(add Wr'dst Rd'a Rd'b)`. 
@@ -473,9 +474,15 @@ Jumping to a label is always safer than a manual skip.
 ; The arguments are passed as argX. Return values are stored in resX registers.
 (call PROC Rd...)
 
-; Exit the current routine with return values
+; Spawn a coroutine. The handle is stored in the output register.
+(spawn Wr'handle PROC Rd...)
+
+; Exit the current routine (or coroutine) with return values
 (ret Rd...)
 
+; Wait for a coroutine to complete, read its return values and delete it.
+(join @Obj)
+
 ; Generate a run-time fault with a debugger message
 (fault)
 (fault message)