Additional revisions to README.md

[davidkartuzinski]

⚠️ We have stopped merging PRs for now to the Strapi core.


The reason is that we are developing new architecture for the admin panel and for the plugins.

This new architecture will provide stability of the Strapi core as we approach the release of Beta.

We appreciate and welcome all your contributions, but until further notice, please do not submit a PR as it will not be merged.

Furthermore, you will have to rewrite it based on the new architecture.

BETA: Additional revisions to README.md

Additional revisions to the BETA version of the Strapi README.md. Clarifies, edits, add and removes different sections.

Description:

• This corrects minor typos and grammar.
• Adds versions to support OSes
• Ensure all references to BETA are removed.
• Rearranged content to move Heroku One Click below the feature list.
• Deleted Professional Services section
• Other minor clarifications.

My PR is a:

• 💥 Breaking change
• 🐛 Bug fix #issueNumber
• 💅 Enhancement
• 🚀 New feature

Main update on the:

• Admin
• Documentation
• Framework
• Plugin

Manual testing done on the following databases:

• Not applicable
• MongoDB
• MySQL
• Postgres
• SQLite

[derrickmehaffy]

LGTM

[alexandrebodin]

Great work