feat: add icons and command tools (like nix)

README.md

@@ -15,7 +15,7 @@
 ## Use the template
 
 ```bash
-nix flake new myapp -t 'git+https://git.dgren.dev/eric/nix-flake-lib?ref=v3.0.0#default' --refresh
+nix flake new myapp -t 'git+https://git.dgren.dev/eric/nix-flake-lib?ref=refs/tags/v3.0.0#default' --refresh
 ```
 
 ## Use the library
@@ -23,7 +23,7 @@ nix flake new myapp -t 'git+https://git.dgren.dev/eric/nix-flake-lib?ref=v3.0.0#
 Add this flake input:
 
 ```nix
-inputs.repo-lib.url = "git+https://git.dgren.dev/eric/nix-flake-lib?ref=v3.0.0";
+inputs.repo-lib.url = "git+https://git.dgren.dev/eric/nix-flake-lib?ref=refs/tags/v3.0.0";
 inputs.repo-lib.inputs.nixpkgs.follows = "nixpkgs";
 ```
 
@@ -49,10 +49,10 @@ outputs = { self, nixpkgs, repo-lib, ... }:
 
     perSystem = { pkgs, system, ... }: {
       tools = [
-        (repo-lib.lib.tools.fromPackage {
+        (repo-lib.lib.tools.fromCommand {
           name = "Nix";
-          package = pkgs.nix;
           version.args = [ "--version" ];
+          command = "nix";
         })
       ];
 
@@ -73,7 +73,7 @@ outputs = { self, nixpkgs, repo-lib, ... }:
 
 ## Tool banners
 
-Tools are declared once, from packages. They are added to the shell automatically and rendered in the startup banner.
+Tools are declared once. Package-backed tools are added to the shell automatically, and both package-backed and command-backed tools are rendered in the startup banner.
 
 ```nix
 (repo-lib.lib.tools.fromPackage {
@@ -86,6 +86,16 @@ Tools are declared once, from packages. They are added to the shell automaticall
 
 Required tools fail shell startup if their version probe fails. This keeps banner output honest instead of silently hiding misconfiguration.
 
+When a tool should come from the host environment instead of `nixpkgs`, use `fromCommand`:
+
+```nix
+(repo-lib.lib.tools.fromCommand {
+  name = "Nix";
+  command = "nix";
+  version.args = [ "--version" ];
+})
+```
+
 ## Purity model
 
 The default path is pure: declare tools and packages in Nix, then let `mkRepo` assemble the shell.