remind people to update the hash

And offer help since it's pretty easy but impossible if you don't have
Nix installed.

Cargo.toml

@@ -7,9 +7,13 @@ homepage = "https://conduit.rs"
 repository = "https://gitlab.com/famedly/conduit"
 readme = "README.md"
 version = "0.6.0-alpha"
-rust-version = "1.64"
 edition = "2021"
 
+# When changing this, change the hash near the text "THE rust-version HASH" in
+# `/flake.nix` too. If you don't have Nix installed or otherwise don't know how
+# to do this, ping `@charles:computer.surgery` in the matrix room.
+rust-version = "1.64"
+
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]

flake.nix

@@ -32,8 +32,7 @@
         # Use the Rust version defined in `Cargo.toml`
         channel = cargoToml.package.rust-version;
 
-        # This will need to be updated when `package.rust-version` is changed in
-        # `Cargo.toml`
+        # THE rust-version HASH
         sha256 = "sha256-8len3i8oTwJSOJZMosGGXHBL5BVuGQnWOT2St5YAUFU=";
       };