Readme changed with the new way of getting access token method

[devopsfactory-in]

Description

The existing method to get the access token from Launch browser console is no longer available. So, updated the readme with the new method 'copy(adobeIMS.getAccessToken())'

Related Issue

https://github.com/adobe/reactor-sdk-javascript/issues/53

Motivation and Context

Correction in technical documentation. So, everyone can continue using the library without blocking.

How Has This Been Tested?

N/A

Screenshots (if appropriate):

Types of changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x ] I have signed the Adobe Open Source CLA.
• [x ] My code follows the code style of this project.
• [ x] My change requires a change to the documentation.
• [ x] I have updated the documentation accordingly.
• [ x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

[thebenrob]

Gonna close this one since it's a duplicate of #55 and I saw and reviewed that one first.