fixes #89 -- add saga docs

[JoshMcCullough]

Thank you for your contribution! :thumbsup:

Please makes sure that these checkboxes are checked before submitting your PR, thank you!

• [ x ] Rebase before creating a PR to keep commit history clean
• [ - ] Clear node_modules and reinstall all the dependencies: npm run reinstall
• [ - ] Run checker npm script: npm run check

Extra checklist:

• [ x ] Always add some description and refer to all the related issues using # tag

For bugfixes:

• [ - ] Add at least one unit test to cover the bug that have been fixed

For new feature:

• [ - ] Update API docs
• [ - ] Add examples to demonstrate new feature
• [ - ] Add type unit tests
• [ - ] Add runtime unit tests

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Added sagas documentation. Tried to follow existing documentation samples. Now, where's my $20? ;-)