Update compiler/rustc_session/src/config.rs

Co-authored-by: León Orell Valerian Liehr <[email protected]>

Author: xizheyin

compiler/rustc_session/src/config.rs

@@ -1679,7 +1679,7 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
             "",
             "cfg",
             "Configure the compilation environment.\n\
-                SPEC supports the syntax `<NAME>[=\"VALUE\"]`.",
+                SPEC supports the syntax `<NAME>[=\"<VALUE>\"]`.",
             "<SPEC>",
         ),
         opt(Stable, Multi, "", "check-cfg", "Provide list of expected cfgs for checking", "<SPEC>"),