add nvmrc for easier, more stable development

[circAssimilate]

When first setting up the repo I had some troubles with yarn start:examples and yarn build:watch not working. After trying a few different types of node I found the latest stable version (v12.13.1) on https://nodejs.org/en/ worked well. This PR will add an .nvmrc file for those who use Node Version Manager to make development across several projects more reliable and less frustrating. Totally open to another node version if the one for @praneshr's env is different that v12.13.1.

[praneshr]

@circAssimilate This is very useful. But, I don't think everyone uses nvm. Even I use n for managing my node versions. Can we go with a generic approach to address this? Can we try engines in package.json? If you can address this quickly, I can include this change with v3.0 :)

Thanks again for your contributions.

[circAssimilate]

No probo, @praneshr. Unfortunately, after doing a bit of looking I couldn't find a clear way to actually make use of package.json's engine key. Have you come across any standard way? Totally up to you of course but I feel it's ok to be prescriptive with a node version manager (I'm ok with nvm or n) as long as it's standard - at least until NPM makes it as easy (or I learn a way they've already provided). Happy to make the PR if you can point me in the right direction solely using NPM!

[praneshr]

Hi @circAssimilate, thanks for the reply. However, I've fixed it myself by adding engines.

Check #58

[circAssimilate]

Thanks, @praneshr! It may be helpful to add a recommended approach to using that engine spec via the command line - but glad it's at least there for manual reference.