add notes on unsupported features

README.md

@@ -63,6 +63,20 @@ Then, run the test with
 RUSTFLAGS="--cfg loom" cargo test --test buggy_concurrent_inc --release
 ```
 
+## C11 Memory model coverage
+Loom currently does not implement the full C11 memory model.
+Here is the (incomplete) list of unsupported features.
+* `SeqCst` accesses (e.g. `load`, `store`, ..):
+  They are are regarded as `AcqRel`. That is, they impose weaker
+  synchronization, causing Loom to generate false alarms (not complete). See
+  [#180](/~https://github.com/tokio-rs/loom/issues/180) for example. On the other
+  hand, `fence(SeqCst)` is supported.
+* Load buffering behavior:
+  Loom does not explore some executions that are possible in the C11 memory
+  model. That is, there can be a bug in the checked code even if Loom says
+  there is no bug (not sound).  See the `load_buffering` test case in
+  `tests/litmus.rs`.
+
 ## License
 
 This project is licensed under the [MIT license](LICENSE).