update README

README.md

@@ -3,10 +3,55 @@
 
 ## Usage
 
-> [!INFO]
+### Install nix
-> See [sloanelybutsurely/nix-darwin](https://github.com/sloanelybutsurely/nix-darwin) for complete setup instructions
 
-## TODO
+I've used the [DeterminateSystems installer](https://github.com/DeterminateSystems/nix-installer?tab=readme-ov-file#the-determinate-nix-installer).
 
-- [ ] Move `sloanelybutsurely/nix-darwin` into this repo
+### Install Homebrew
-- [ ] Add `bootstrap` scripts to install nix and setup `nix-darwin`
+
+_(This is mostly to use casks to install GUI applications.)_
+
+Use the instructions on [brew.sh](https://brew.sh/).
+
+### Run first time setup
+
+If the current hostname and username of are already defined in the [nix-darwin config](./.config/nix-darwin) you can run `nix-darwin` to bootstrap the machine.
+
+```sh
+nix run nix-darwin -- switch --flake 'github:sloanelybutsurely/dotfiles?dir=.config/nix-darwin'
+```
+
+<details>
+<summary>New hostname or username</summary>
+
+If you're setting up a brand new machine or using a new username you'll have to clone this repo and update the `nix-darwin` config to include the new hostname and/or username.
+
+If you commit and push these changes you can continue these instructions from the above.
+
+If you want to bootstrap from a local copy of this repo you can run `nix-darwin`:
+
+```sh
+nix run nix-darwin -- switch --flake /path/to/.config/nix-darwin
+```
+
+</details>
+
+
+### Set shell
+
+```sh
+chsh -s /run/current-system/sw/bin/fish
+```
+
+### Reboot the machine
+
+This will let the new shell take hold.
+
+### Clone remaining dotfiles and nix-darwin
+
+Once setup you can fetch a local copy of the nix-darwin config and some remaining dotfiles.
+
+```sh
+# yadm should have been installed by 
+yadm clone git@github.com:sloanelybutsurely/dotfiles.git
+```