better doc for schema

tracim/views/contents_api/html_document_controller.py

     @hapic.input_path(WorkspaceAndContentIdPathSchema())
     @hapic.input_body(HtmlDocumentModifySchema())
     @hapic.output_body(HtmlDocumentContentSchema())
-    def update_html_document(self, context, request: TracimRequest, hapic_data=None):
+    def update_html_document(self, context, request: TracimRequest, hapic_data=None):  # nopep8
         """
         update_html_document
         """

tracim/views/core_api/schemas.py

     )
     label = marshmallow.fields.Str(example='Intervention Report 12')
     content_type = marshmallow.fields.Str(
-        example='htmlpage',
+        example='html-content',
         validate=OneOf([content.slug for content in CONTENT_DEFAULT_TYPE]),
     )
     sub_content_types = marshmallow.fields.List(
 
 
 class ThreadContentSchema(ContentSchema):
+    content_type = marshmallow.fields.Str(
+        example='thread',
+        validate=OneOf([content.slug for content in CONTENT_DEFAULT_TYPE]),
+    )
     raw_content = marshmallow.fields.String('Description of Thread')
 
 
 class HtmlDocumentContentSchema(ContentSchema):
+    content_type = marshmallow.fields.Str(
+        example='html-content',
+        validate=OneOf([content.slug for content in CONTENT_DEFAULT_TYPE]),
+    )
     raw_content = marshmallow.fields.String('<p>Html page Content !</p>')
 
 #####
 
 
 class ThreadRevisionSchema(RevisionSchema):
+    content_type = marshmallow.fields.Str(
+        example='thread',
+        validate=OneOf([content.slug for content in CONTENT_DEFAULT_TYPE]),
+    )
     raw_content = marshmallow.fields.String('Description of Thread')
 
 
 class HtmlDocumentRevisionSchema(RevisionSchema):
+    content_type = marshmallow.fields.Str(
+        example='html-content',
+        validate=OneOf([content.slug for content in CONTENT_DEFAULT_TYPE]),
+    )
     raw_content = marshmallow.fields.String('<p>Html page Content !</p>')