UserInfoDto: Add doc comments

Signed-off-by: David Mehren <git@herrmehren.de>

src/users/user-info.dto.ts

@@ -4,15 +4,41 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
+import { ApiProperty } from '@nestjs/swagger';
 import { IsString } from 'class-validator';
 
 export class UserInfoDto {
+  /**
+   * The username
+   * @example "john.smith"
+   */
   @IsString()
   userName: string;
+
+  /**
+   * The display name
+   * @example "John Smith"
+   */
   @IsString()
   displayName: string;
+
+  /**
+   * URL of the profile picture
+   * @example "https://hedgedoc.example.com/uploads/johnsmith.png"
+   */
+  @ApiProperty({
+    format: 'uri',
+  })
   @IsString()
   photo: string;
+
+  /**
+   * Email address of the user
+   * @example "john.smith@example.com"
+   */
+  @ApiProperty({
+    format: 'email',
+  })
   @IsString()
   email: string;
 }