Add tracking issue for cf-protection to unstable book

Author: wesleywiser

src/doc/unstable-book/src/compiler-flags/cf-protection.md

@@ -1,5 +1,9 @@
 # `cf-protection`
 
+The tracking issue for this feature is: [#93754](https://github.com/rust-lang/rust/issues/93754).
+
+------------------------
+
 This option enables control-flow enforcement technology (CET) on x86; a more detailed description of
 CET is available [here]. Similar to `clang`, this flag takes one of the following values: