Updated GB_set_rewind_length (markdown)

GB_set_rewind_length.md

@@ -6,8 +6,15 @@ In `rewind.h`
 
 ## Description
 
-TBD
+Sets the time limit, in seconds, of the emulator instance's rewind buffer. Changing the buffer's length implicitly [[resets it|GB_rewind_reset]].
+
+In order for the debugger to support the `backstep` command, a non-zero rewind length is required.
 
 ## Thread Safety
 
 `GB_set_rewind_length` must not be called if the instance is being run in another thread, but may be called from the current one (via a callback).
+
+## See Also
+
+* [[GB_rewind_pop]]
+* [[GB_rewind_reset]]