Document some major known limitations of Eyra.

README.md

@@ -73,9 +73,18 @@ Hello, world!
 [TRACE origin::program] `origin_main` returned `0`
 [TRACE origin::thread] Thread[51383] calling `at_thread_exit`-registered function
 [TRACE origin::thread] Thread[51383] calling `at_thread_exit`-registered function
-[TRACE origin::program] Program exiting
+[TRACE origin::program] Program exiting with status `0`
 ```
 
+## Known Limitations
+
+Known limitations in `Eyra` include:
+
+ - Dynamic linking isn't implemented yet.
+ - Many libc C functions that aren't typically needed by most Rust programs
+   aren't implemented yet.
+ - Enabling LTO doesn't work yet.
+
 ## Background
 
 Eyra is similar to [Mustang] and uses the same underlying code, but instead