Add a flake template for Markdown notes

[Sridhar Ratnakumar]

Should initialize the current folder of .md files with flake.nix of https://github.com/srid/emanote-template - and possibly another template that includes the whole jazz (.vscode, .github, index.yaml, index.md)

For use with https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake-init.html

[Sridhar Ratnakumar]

Use this opportunity to move https://github.com/srid/emanote/blob/master/nix/emanote.nix to its own repo, as flake-parts module cum template.

[Shivaraj B H]

@srid If it is still a consideration to move the flakeModule and templates to a repo of their own, I can close the PR above and raise it in the right one.

[Sridhar Ratnakumar]

Nah, it is fine. Let's keep it all in this repo.