Updated guidance on web part properties with image source (SharePoint#819)

Author: waldekmastykarz

docs/spfx/web-parts/guidance/integrate-web-part-properties-with-sharepoint.md

@@ -66,4 +66,4 @@ If you specify the web part property as `isSearchablePlainText`, it will be incl
 
 When a web part property is defined as `isHtmlString`, SharePoint will first of all remove any unsafe HTML, such as `script` tags, from the property value. The HTML that remains can be considered safe to render on a page. If the value contains any URLs pointing to files stored in SharePoint, as soon as one of these files is renamed or moved, SharePoint will automatically update the URL stored in the web part property. This significantly simplifies managing URLs across all web parts and pages in your tenant. HTML web part properties are also searchable, so users can look for any keywords included in the property value.
 
-Property value types `isImageSource` and `isLink` are meant to be used for web part properties than include nothing else but a link to an image or a file stored in SharePoint. In both cases, SharePoint Search includes the content in the full-text index and keeps the specified URL up-to-date in case the referenced file is renamed or moved. Additionally, image sources may get additional processing to help images download faster.
+Property value types `isImageSource` and `isLink` are meant to be used for web part properties than include nothing else but a link to an image or a file stored in SharePoint. In both cases, SharePoint Search includes the content in the full-text index and keeps the specified URL up-to-date in case the referenced file is renamed or moved. Additionally, image sources may get additional processing to help images download faster. If the page has a title image and the image is amongst the first 5 images on the page or the image is in the first two rows on the page, the image will be preloaded.