add instructions to run individual e2e tests

[fedekunze]

Description:

run all e2e tests:

$ yarn test:e2e

We need to add instructions to run single a e2e test on our README:

$ yarn run pack
$ npx tape test/e2e/wallet.js

[sabau]

What if we keep the same command to accept something like this:

yarn test:e2e
TEST=test/e2e/init.js yarn test:e2e

This can work with no problem on *nix machines. If Windows should be covered, do we have a Windows machine to check what happens there?

[faboweb]

If Windows should be covered, do we have a Windows machine to check what happens there?

I can recommend VirtualBox to cover Windows.