Lost text re-added

Author: jesusprubio

compiler/rustc_error_codes/src/error_codes/E0547.md

@@ -1,6 +1,14 @@
+The `issue` value is missing in a stability attribute.
+
+Erroneous code example:
+
+```compile_fail,E0547
+#![feature(staged_api)]
 #![stable(since = "1.0.0", feature = "test")]
+
 #[unstable(feature = "_unstable_fn")] // invalid
 fn _unstable_fn() {}
+
 #[rustc_const_unstable(feature = "_unstable_const_fn")] // invalid
 fn _unstable_const_fn() {}
 ```
@@ -10,8 +18,10 @@ To fix the issue you need to provide the `issue` field.
 ```
 #![feature(staged_api)]
 #![stable(since = "1.0.0", feature = "test")]
+
 #[unstable(feature = "_unstable_fn", issue = "none")] // ok!
 fn _unstable_fn() {}
+
 #[rustc_const_unstable(
     feature = "_unstable_const_fn",
     issue = "none"