doc(init): Explain params spec

doc/src/om/init.md

@@ -3,7 +3,7 @@
 > [!IMPORTANT]
 > `om init` is available as a beta-feature.
 
-The `om init` command provides a better `nix flake init` experience. Specifically, it provides:
+The `om init` command provides a better [`nix flake init`](https://nix.dev/manual/nix/2.18/command-ref/new-cli/nix3-flake-init) experience. Specifically, it provides:
 
 1. a registry of flake templates that you can choose from
 2. support for template paramters that can be filled in by the user
@@ -22,3 +22,34 @@ In future, you would be able to directly initialize a project from a git reposit
 
 > [!NOTE]
 > The specification for template paramters are yet to be finalized. Until, then the relevant parameter configuration is tied to the registry in omnix repo. See [`crates/omnix-init/registry`](https://github.com/juspay/omnix/tree/main/crates/omnix-init/registry).
+
+## Configuration spec {#spec}
+
+Omnix templates can be defined by adding a `om.template` flake output. This should be an attrset of templates. The value should contain the keys `template` (referring to original flake template) as well as `params`, defined as follows:
+
+There are two kinds of params. **String params** are defined as follows:
+
+```nix
+{
+  name = "package-name";
+  description = "Name of the Rust package";
+  placeholder = "rust-nix-template";
+}
+```
+
+Here, when prompting for this param, the user-provided value if any will replace the given `placeholder` text across all files in the template.
+
+**Boolean params** are defined as follows:
+
+```nix
+{
+  name = "vscode";
+  description = "Include the VSCode settings folder (./.vscode)";
+  paths = [ ".vscode" ];
+  value = true;
+}
+```
+
+Here, if the user enables this param, the path globs specified in `paths` will be retained in the template. Otherwise, the paths will be deleted. The `value` key provides a default value; which key is supported for string params as well.
+
+Both parameter types are distinguished by the presence of the relevant keys (`placeholder` for string, `paths` for boolean).