Insert comma after "At Instagram" in readme.md

Summary:
Issue fixed: Instagram#762

- [x] All tests pass. Demo project builds and runs.
- [x] I added tests, an experiment, or detailed why my change isn't tested.
- [x] I added an entry to the `CHANGELOG.md` for any breaking changes, enhancements, or bug fixes.
- [x] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md)
Closes Instagram#780

Differential Revision: D5129315

Pulled By: rnystrom

fbshipit-source-id: d63e37c75ba633899ea8759c7c9c1baf023b1e2b

README.md

@@ -87,11 +87,11 @@ You can find [the docs here](https://instagram.github.io/IGListKit). Documentati
 
 ## Vision
 
-For the long term goals and "vision" of `IGListKit`, please read our [Vision](https://github.com/Instagram/IGListKit/blob/master/Guides/VISION.md) doc.
+For the long-term goals and "vision" of `IGListKit`, please read our [Vision](https://github.com/Instagram/IGListKit/blob/master/Guides/VISION.md) doc.
 
 ## Contributing
 
-Please see the [CONTRIBUTING](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md) file for how to help. At Instagram we sync the open source version of `IGListKit` daily, so we're always testing the latest changes. But that requires all changes be thoroughly tested and follow our style guide.
+Please see the [CONTRIBUTING](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md) file for how to help. At Instagram, we sync the open source version of `IGListKit` daily, so we're always testing the latest changes. But that requires all changes be thoroughly tested and follow our style guide.
 
 We have a set of [starter tasks](https://github.com/Instagram/IGListKit/issues?q=is%3Aissue+is%3Aopen+label%3Astarter-task) that are great for beginners to jump in on and start contributing.