README: fix capitalization of 'ISO'

Author: kekrby

README.md

@@ -4,7 +4,7 @@ This flake can be used to build a NixOS installer that can be used with T2 Macs.
 
 Prebuilt installers are available in the [releases page](https://github.com/kekrby/nixos-t2-iso/releases).
 
-This repo provides two isos:
+This repo provides two ISOs:
 * `t2-iso-minimal`
 * `t2-iso-gnome`
 
@@ -19,7 +19,7 @@ nix build .#t2-iso-minimal
 
 You need to have `nix` installed on a **Linux** host. If you are on macOS, you can use `podman` or `docker` with the `nixos/nix` image.
 
-As iso files can be quite large depending on their content, they are split into multiple parts. You can join them with this command after downloading all the files for the variant you want:
+As ISO files can be quite large depending on their content, they are split into multiple parts. You can join them with this command after downloading all the files for the variant you want:
 ```
 cat t2-iso-<variant>.iso-part-* > t2-iso-<variant>.iso
 ```