Updates to the way we present Jetpack features.

- simpler tag line
- new section including feature groups
- shortening text of the long feature list bullet points
- removal of various distracting links
- fix various typos
- link to installation video walkthrough
Revert "Updates to the way we present Jetpack features."

This reverts commit 26ff063a32401e225bb444ad748223d94418bc5d.
Updates to the way we present Jetpack features.

- simpler tag line
- new section including feature groups
- shortening text of the long feature list bullet points
- removal of various distracting links
- fix various typos
- link to installation video walkthrough
Tweak to tag line.
Adds Oxford comma!
Merge pull request #1229 from Automattic/updated-readme

Updated readme