add EbrCell to trophy case

Author: RalfJung

README.md

@@ -259,6 +259,7 @@ Definite bugs found:
 * [`getrandom` calling the `getrandom` syscall in an invalid way](https://github.com/rust-random/getrandom/pull/73)
 * [`Vec`](https://github.com/rust-lang/rust/issues/69770) and [`BTreeMap`](https://github.com/rust-lang/rust/issues/69769) leaking memory under some (panicky) conditions
 * [Memory leak in `beef`](https://github.com/maciejhirsz/beef/issues/12)
+* [Invalid use of undefined memory in `EbrCell`](https://github.com/Firstyear/concread/commit/b15be53b6ec076acb295a5c0483cdb4bf9be838f#diff-6282b2fc8e98bd089a1f0c86f648157cR229)
 
 Violations of [Stacked Borrows] found that are likely bugs (but Stacked Borrows is currently just an experiment):