Add docs

docsite/source/basics/working-with-schemas.html.md

@@ -109,4 +109,4 @@ result.error?([:tags, 1])
 ### Learn more
 
 - [Customizing messages](docs::error-messages)
-- [Validation hints](docs::extensions/hints)
+- [Validation hints](docs::extensions/hints)

docsite/source/extensions.html.md

@@ -6,6 +6,7 @@ sections:
   - hints
   - info
   - monads
+  - json_schema
 ---
 
 `dry-schema` can be extended with extension. Those extensions are loaded with `Dry::Schema.load_extensions`.
@@ -15,3 +16,4 @@ Available extensions:
 - [Hints](docs::extensions/hints)
 - [Info](docs::extensions/info)
 - [Monads](docs::extensions/monads)
+- [JSON Schema](docs::extensions/json_schema)

docsite/source/extensions/json_schema.html.md

@@ -0,0 +1,38 @@
+---
+title: JSON Schema
+layout: gem-single
+name: dry-schema
+---
+
+The `:json_schema` extension allows you to generate a valid [JSON Schema](https://json-schema.org/) from a `Dry::Schema`. JSON Schema is a widely used standard, so this unlocks many possibilities.
+
+```ruby
+Dry::Schema.load_extensions(:json_schema)
+
+UserSchema = Dry::Schema.JSON do
+  required(:email).filled(:string, min_size?: 8)
+
+  optional(:age).filled(:integer)
+end
+
+UserSchema.json_schema 
+# {
+#   "type": "object",
+#   "properties": {
+#     "email": {
+#       "type": "string",
+#       "minLength": 8
+#     },
+#     "age": {
+#       "type": "integer"
+#     },
+#   "required": ["email"] 
+# }
+```
+
+### Learn more
+
+- [Official JSON Schema docs](https://json-schema.org/)
+- [Auto-generate forms with React + JSON Schema](https://github.com/rjsf-team/react-jsonschema-form))
+- [Integrate with other languages more easily](https://json-schema.org/implementations.html)
+