Add a readme for Json Schema

common/changes/@typespec/json-schema/json-schema-readme_2023-06-28-19-05.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@typespec/json-schema",
+      "comment": "",
+      "type": "none"
+    }
+  ],
+  "packageName": "@typespec/json-schema"
+}

packages/json-schema/README.md

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+# TypeSpec JSON Schema Emitter
+
+This package provides [TypeSpec](https://github.com/microsoft/TypeSpec) support for emitting JSON Schema version `2020-12` from TypeSpec definitions. It also provides [decorators for adding JSON Schema constraints](https://microsoft.github.io/typespec/standard-library/json-schema/reference/decorators). The emitter supports either YAML or JSON output and can be configured to emit one file per schema or bundle all schemas in to a single file.
+
+## Installation
+
+```bash
+npm install @typespec/json-schema
+```
+
+## Usage
+
+Add the `@jsonSchema` decorator to any types or namespaces you want to emit as JSON Schema.
+
+```TypeSpec
+import "@typespec/json-schema";
+
+using TypeSpec.JsonSchema;
+
+@jsonSchema
+namespace Example;
+
+model Car {
+  make: string;
+  model: string;
+}
+```
+
+To emit JSON Schema, use either of the following:
+
+1. Via the command line
+
+```bash
+tsp compile . --emit @typespec/json-schema
+```
+
+2. Via the config
+
+Add the following to the `tspconfig.yaml` file.
+
+```yaml
+emitters:
+  @typespec/json-schema: true
+```
+
+For more information, consult the [JSON Schema documentation](https://microsoft.github.io/typespec/standard-library/json-schema/reference).
+
+## Emitter options
+
+### `file-type`
+
+**Type:** `"yaml" | "json"`
+
+Serialize the schema as either yaml or json.
+
+### `int64-strategy`
+
+**Type:** `"string" | "number"`
+
+How to handle 64 bit integers on the wire. Options are:
+
+- string: serialize as a string (widely interoperable)
+- number: serialize as a number (not widely interoperable)
+
+### `bundleId`
+
+**Type:** `string`
+
+When provided, bundle all the schemas into a single json schema document with schemas under $defs. The provided id is the id of the root document and is also used for the file name.
+
+### `emitAllModels`
+
+**Type:** `boolean`
+
+When true, emit all model declarations to JSON Schema without requiring the @jsonSchema decorator.
+
+### `emitAllRefs`
+
+**Type:** `boolean`
+
+When true, emit all references as json schema files, even if the referenced type does not have the `@jsonSchema` decorator or is not within a namespace with the `@jsonSchema` decorator.
+
+## See also
+
+- [Json Schema Emitter Documentation](https://microsoft.github.io/typespec/standard-library/json-schema/reference)
+- [TypeSpec Getting Started](https://github.com/microsoft/typespec#getting-started)
+- [TypeSpec Website](https://microsoft.github.io/typespec)