feat: Forward method TBATS/AutoTBATS

[MMenchero]

• Added forward method for TBATS and AutoTBATS.
• Included example of forward method.
• Added TBATS and AutoTBATS to README.
• Fixed minor issue with AutoTBATS docs

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}