Recommend -Zshare-generics=false

opt-level=z|s implicitly enables -Zshare-generics=true, which sometimes has a positive and sometimes has a negative impact.

Author: Noratrieb

README.md

@@ -72,6 +72,9 @@ opt-level = "z"  # Optimize for size.
 > It is recommended to experiment with different levels to find the right balance for your project.
 > There may be surprising results, such as ... the `"s"` and `"z"` levels not being necessarily
 > smaller.
+>
+> When using `"z"`, you can also try the `-Zshare-generics=false` rustc flag with the nightly toolchain
+> (via RUSTFLAGS).
 
 # Enable Link Time Optimization (LTO)
 
@@ -438,4 +441,4 @@ use std::alloc::System;
 
 #[global_allocator]
 static A: System = System;
-```
+```