Add a known that this is a known limitation

Author: jackh726

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_relation.rs

@@ -69,6 +69,7 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
                     }
                     _ => {}
                 }
+                err.note("this is a known limitation that will be removed in the future (see issue #100013 <https://github.com/rust-lang/rust/issues/100013> for more information)");
                 Some(err)
             }
 

src/test/ui/generic-associated-types/bugs/issue-100013.stderr

@@ -18,6 +18,7 @@ note: ...must outlive the lifetime defined here
    |
 LL |         let x = None::<I::Future<'_, '_>>; // a type referencing GAT
    |                                  ^^
+   = note: this is a known limitation that will be removed in the future (see issue #100013 <https://github.com/rust-lang/rust/issues/100013> for more information)
 
 error: lifetime bound not satisfied
   --> $DIR/issue-100013.rs:23:5
@@ -40,6 +41,7 @@ note: ...must outlive the lifetime defined here
    |
 LL | fn call2<'a, 'b, I: FutureIterator>() -> impl Send {
    |          ^^
+   = note: this is a known limitation that will be removed in the future (see issue #100013 <https://github.com/rust-lang/rust/issues/100013> for more information)
 
 error: lifetime may not live long enough
   --> $DIR/issue-100013.rs:25:17
@@ -74,6 +76,7 @@ note: ...must outlive the lifetime defined here
    |
 LL | fn call3<'a: 'b, 'b, I: FutureIterator>() -> impl Send {
    |          ^^
+   = note: this is a known limitation that will be removed in the future (see issue #100013 <https://github.com/rust-lang/rust/issues/100013> for more information)
 
 error: aborting due to 4 previous errors