update documentation (prebid#6354)

Author: ym-aaron

dev-docs/bidders/yieldmo.md

@@ -40,7 +40,7 @@ The Yieldmo adapter supports in-stream video as of Prebid v4.18. Out-stream will
 | `maxduration`     | required | Maximum ad duration in seconds                         | `20`            | `integer` |
 | `minduration`     | optional | Minimum ad duration in seconds                         | `5`             | `integer` |
 | `pos`             | optional | Ad position on screen; see [OpenRTB 2.5 specification](https://www.iab.com/wp-content/uploads/2016/03/OpenRTB-API-Specification-Version-2-5-FINAL.pdf), List 5.4 for more details | `1`  | `integer` |
-| `startdelay`      | required for in-stream | Duration offset (in second) from the start of the content for showing the video ad before the start of the Video. Pre-roll: `0` (default); Mid-roll: `>0`; Default mid-roll: `-1`; Post-roll: `-2`; <br/><br/> For out-stream is' always `0`| `5`  | `integer` |
+| `startdelay`      | optional | Start delay of the video ad in seconds. Values follow OpenRTB 2.5 §5.12: `0` = Pre-Roll; `>0` = Mid-Roll (value is the start delay); `-1` = Generic Mid-Roll; `-2` = Generic Post-Roll. | `5`  | `integer` |
 | `protocols`       | required | Supported video bid response protocols. VAST 1.0: `1`; VAST 2.0: `2`; VAST 3.0: `3`; VAST 1.0 Wrapper: `4`; VAST 2.0 Wrapper: `5`; VAST 3.0 Wrapper: `6`; | `[2, 3]`        | `Array<integer>` |
 | `api`             | required | API frameworks supported. VPAID 1.0: `1`; VPAID 2.0: `2`; MRAID-1: `3`; ORMMA: `4`; MRAID-2: `5`; MRAID-3: `6`;                                         | `[1, 2]`        | `Array<integer>` |
 | `playbackmethod`  | required | Playback methods that may be in use; see [OpenRTB 2.5 specification](https://www.iab.com/wp-content/uploads/2016/03/OpenRTB-API-Specification-Version-2-5-FINAL.pdf), List 5.10 for more details. Out-stream is only always `2` | `[2,6]`  | `Array<integer>` |