Add note to README that this project is looking for contributors and/or will get deprecated

[adietish]

We're lacking the people to work actively on this project. We're therefore looking for contributors and will deprecate this plugin on the long run.

[albertocavalcante]

@adietish - What is expected and what the process look like to become a maintainer?

[rcjsuen]

We're therefore looking for contributors and will deprecate this plugin on the long run.

What is the fate of the redhat-developer/yaml-language-server? Is that project in danger of being deprecated/archived?