Mentioned sync and abort in README

README.md

@@ -13,10 +13,17 @@ WIP.  Defining and running simple code, loading/compiling secondary files.
 nForth is not ANS (or anything) compliant.  Major deviations:
 
 ### Always Compile
-To avoid the whole state morass, nForth is *always* in compile mode.  Text is parsed, compiled, executed, and erased.  Defining words manipulate the execution and erasure points.No more [IF] and such.  [ ... ] may be used to group compile a group of words as a single unit:
+To avoid the whole state morass, nForth is *always* in compile mode.  Text is parsed and compiled.  To actually execute anything, surround the code with square braces (such code will be erased after execution).
 ```
 OK> [ " Hello" type cr ]
 ```
+### Sync points
+When the dictionary is in a good state, create a checkpoint with `sync` immediate word.  To revert to the previous checkpoint, use `abort`.  `..` is a convenience word that executes all code compiled after the previous checkpoint and deletes it, so instead of the previous example you can do:
+```
+OK> sync
+OK> " Hello" type cr ..
+Hello
+```
 ### Hashes, not Names
 Symbolic names are not stored in the dictionary.  Names are instead hashed at definition time using FNV1a to a 32-bit value and stored in heads.  Dictionary searches are simplified to a 32-bit comparison instead of a string comparison, and heads are always 8 bytes long.