update README

README.md

@@ -15,6 +15,11 @@ inputs.foundation.url = "https://git.auxolotl.org/auxolotl/foundation/archive/ma
 To import this library without using Nix Flakes, you will need to use
 `fetchTarball` and import the library entrypoint.
 
+You probably need to specify the `system` argument, which needs to be one of the supported systems.
+Otherwise, Foundation will default to your current system (builtins.currentSystem).
+Since we only support bootstrapping on 32-bit x86 right now, that probably won't work.
+If you use an unsupported system with Foundation, it will fail to evaluate.
+
 ```nix
 let
     foundation_tarball = builtins.fetchTarball {
@@ -22,13 +27,17 @@ let
         sha256 = "<sha256>";
     };
     foundation = import foundation_tarball {
-        # Specifying a system is optional. By default it will use the current system.
+        # Specifying a system is optional but very likely to be necessary
         system = "i686-linux";
     };
 in
     # ...
 ```
 
+### Supported systems
+
+For now, Aux Foundation only supports bootstrapping for `"i686-linux"`.
+
 ### Bypassing Geoblocking
 
 If you get an error(possibly with different hashes) such as