CouchbaseLite with Xamarin Forms PCL

How to include Couchbase into Xamarin Fotms PCL project?

There is no officially supported way in either 1.x or 2.x. The fastest way is to compile it yourself, or migrate to .NET Standard which has made PCL defunct.

for .NET Standard Projects in Xamarin itself, any documentaion or example how to include couchbase lite?

It’s no different than any other case. Read the getting started docs. It says “UWP Project” but it applies to any .NET project that runs on our supported platforms.