To install just unzip the contents into your Plugins folder. This should create a directory named YoutubeMetadata with the files below.
Archive: YoutubeMetadata.zip
Length Date Time Name
--------- ---------- ----- ----
0 2020-04-19 23:00 YoutubeMetadata/
123392 2020-04-02 10:45 YoutubeMetadata/Google.Apis.Auth.dll
5120 2020-04-02 10:45 YoutubeMetadata/Google.Apis.Auth.PlatformServices.dll
73216 2020-04-02 10:45 YoutubeMetadata/Google.Apis.Core.dll
78848 2020-04-02 10:45 YoutubeMetadata/Google.Apis.dll
293888 2020-04-06 08:12 YoutubeMetadata/Google.Apis.YouTube.v3.dll
18944 2020-04-19 22:59 YoutubeMetadata/Jellyfin.Plugin.YoutubeMetadata.dll
693680 2019-11-09 01:56 YoutubeMetadata/Newtonsoft.Json.dll
--------- -------
1287088 8 files
MD5: a14a399410f6449a1f250d51e111915b
SHA256: 9497b1e104161caffa3af87ee5187348a9e04ef40518d1320841378c9d8a345f