[SOL] Improve error message for MSRV

src/cargo/ops/cargo_compile/mod.rs

@@ -496,7 +496,10 @@ pub fn create_bcx<'a, 'gctx>(
 
             let plural = if incompatible.len() == 1 { "" } else { "s" };
             let mut message = format!(
-                "rustc {rustc_version} is not supported by the following package{plural}:\n"
+                "rustc {rustc_version} is not supported by the following package{plural}:\n
+                 Note that this is the rustc version that ships with Solana tools and \
+                 not your system's rustc version. Use `solana-install update` or head \
+                 over to https://docs.solanalabs.com/cli/install to install a newer version.\n",
             );
             incompatible.sort_by_key(|(unit, _)| (unit.pkg.name(), unit.pkg.version()));
             for (unit, msrv) in incompatible {