Consistently recommend priority order of .node-version or .nvmrc

Issue

The fnm project should recommend either .node-version or .nvmrc as a first choice for configuring the Node.js version.

Currently documentation is inconsistent by recommending one or the other as first choice.

Evidence

1. The page https://www.fnmnode.com/guide/nvmrc.html mentions .nvmrc before .node-version.
2. The page https://www.fnmnode.com/ mentions .node-version before .nvmrc
3. In the sidebar of the documentation, the heading name is "Version Files (.nvmrc)". There is no heading named ".node-version" and no documentation URL ".../node-version.html" ordered before that.

Recommendation

1. Decide which is the preferred file (perhaps .node-version).
2. Ensure that the software does not treat the preferred file any worse than other files.
   1. Alternative: if we want to have a URL and heading specifically for the .nvmrc file and not for the .node-version file, then in the .nvmrc file specifically say at top "The fnm project recommends to use the .node-version configuration file instead of .nvmrc if there is a choice. This increases portability and is supported by multiple related projects, including nvm."
3. Update all documentation to mention the /node-version.html URL before the /nvmrc.html.