add @Ericson2314 to the Nix team

John has been part of every meeting since the beginning.
He took on a lot of work on behalf of the team, and provided useful suggestions in discussions, advocating for stability, reasonable design decisions, and maintainable code.

He was in general highly productive within the team process, and repeatedly helped us to keep focus on our stated goals.
Specifically, early on he suggested to gather more experience with the team reviews in order derive our values for the project encode a more structured approach to guiding contributions, which is slowly bearing fruit these days.

John is already the contributor with the most code changes to date (only topped by principal author Eelco), and is well-known to be highly knowledgeable about both high-level design and low-level internals of the code base.
He has continued to offer high quality work during the team's operation, which resulted in many pull requests getting merged that further the team's goals.

It is due time for John to be come an official team member and be granted merge access that he will surely exercise with the great care he is known for.

maintainers/README.md

@@ -11,6 +11,7 @@ The goal of the team is to help other people to contribute to Nix.
 - Valentin Gagarin (@fricklerhandwerk)
 - Thomas Bereknyei (@tomberek)
 - Robert Hensing (@roberth)
+- John Ericson (@Ericson2314)
 
 ## Meeting protocol