Add "Usage" to the README

[cowchimp]

Hi.

I think the README could benefit from a short "Usage" section below the "Installation" section.
It should show what you should actually require() in your code - require('request') OR require('request-promise-native').

Thanks.

[nwhitmont]

@analog-nico any update on adding basic usage examples?

[hackhat]

After a while figuring out this lib I can use this. Pretty bad docs.

    import * as request from 'request-promise-native'; // typescript import
    try {
      const res = await request
        .post('http://localhost:1001/register')
        .form({
          name: this.state.name,
          email: this.state.email,
          password: this.state.password,
        })
    } catch (e) {
      console.error(e);
    }

[nwhitmont]

this repo does not appear to be actively maintained. :-(