docs: mention YouTube (#1082)

mention YouTube capture behavior in behavior docs.

---------

Co-authored-by: Ilya Kreymer <ikreymer@users.noreply.github.com>

Author: mistydemeo

docs/docs/user-guide/behaviors.md

@@ -24,6 +24,7 @@ Browsertrix also comes with several 'site-specific' behaviors, which run only on
 - Telegram
 - TikTok
 - Twitter/X
+- YouTube
 
 User-defined custom behaviors are also considered site-specific.
 
@@ -76,6 +77,13 @@ The Facebook behavior is able to automate the following features:
 - Viewing full-size images, audio and video
 - Viewing quoted posts
 
+### YouTube
+
+The YouTube behavior is able to automate the following features:
+
+- Selecting a video format that the crawler will be able to capture in a single stream. Currently, this will be a .mp4 with resolution of <= 320p due to YouTube limitations.
+- Ensuring that video playback has started
+
 ## Enabling Behaviors
 
 To enable built-in behaviors, specify them via a comma-separated list passed to the `--behaviors` option. All behaviors except Autoclick are enabled by default, the equivalent of `--behaviors autoscroll,autoplay,autofetch,siteSpecific`. To enable only a single behavior, such as Autoscroll, use `--behaviors autoscroll`.