37_text.learner: create docments

[marii-moe]

Add documents to 37_text.learner.

See the style guide and contribution guide for more details (links will be added when created).

This requires a moderate familiarity with fastai. This notebook defines the components needed for automatically creating text classification and lm learners for a specific task. Also includes show methods for model interpretation.

Documents progress(only one section):

• [x] Loading a pretrained model
• [ ] Language modeling predictions
• [ ] Learner convenience functions
• [ ] Show methods

[manisnesan]

I will work on this.