* Reorganize readme, add gif
1. Details in 'Getting Pyenv' and 'Setup for your shell' are collapsed. User can expand relevant
sections depending on their platform and shell.
2. 'How It Works' and 'Advanced Configuration' are moved to the bottom of the README.md
just before 'Contributing' section at the end.
3. Added a GIF in the 'Usage' section to showcase
- Listing python versions available for install.
- Installing a specific python version.
- Listing installed python versions.
- Switching to another python version for a directory.
- Testing by moving terminal into the directory and moving back.
* Update GIF to show prefix resolution
* Collapse upgrade notes
* Cross-mention Linux and MacOS instlalation scenarios
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Co-authored-by: Ivan Pozdeev <vano@mail.mipt.ru>
