link to readme in the build utils llvm error message more (#373)

Signed-off-by: xermicus <[email protected]>

Author: xermicus

crates/build-utils/src/lib.rs

@@ -6,16 +6,18 @@ pub const REVIVE_LLVM_HOST_PREFIX: &str = "LLVM_SYS_181_PREFIX";
 /// The revive LLVM target dependency directory prefix environment variable.
 pub const REVIVE_LLVM_TARGET_PREFIX: &str = "REVIVE_LLVM_TARGET_PREFIX";
 
+/// The revive LLVM host tool help link.
+pub const REVIVE_LLVM_BUILDER_HELP_LINK: &str =
+    "https://github.com/paritytech/revive?tab=readme-ov-file#building-from-source";
+
 /// Constructs a path to the LLVM tool `name`.
 ///
 /// Respects the [`REVIVE_LLVM_HOST_PREFIX`] environment variable.
 pub fn llvm_host_tool(name: &str) -> std::path::PathBuf {
     std::env::var_os(REVIVE_LLVM_HOST_PREFIX)
         .map(Into::<std::path::PathBuf>::into)
         .unwrap_or_else(|| {
-            panic!(
-                "install LLVM using the revive-llvm builder and export {REVIVE_LLVM_HOST_PREFIX}",
-            )
+            panic!("install LLVM using the revive-llvm builder and export '{REVIVE_LLVM_HOST_PREFIX}'; see also: {REVIVE_LLVM_BUILDER_HELP_LINK}")
         })
         .join("bin")
         .join(name)