Well, the diff is not nice, so I'll summarize the changes for humans.

General changes:

* Moved patch submission and so on to the end of the document.
* Reformatted to usual 80 columns, inlined and actualized links.
* Reformatted lists: start from a capital letter, end with a period.
* Minor wording tweaks to make it sound better.

Badges:

* Travis CI and GitLab CI -> GitHub Actions.
* Removed Slack and Gitter.
* Google Groups -> GitHub Discussions.
* Added Stack Overflow.

Define Tarantool as in-memory computing platform as on the website.

Added license information.

Appserver:

* Rewrote the sentence regarding compatibility with Lua 5.1 and
  highlighted key LuaJIT features instead. There are doubts within the
  team about declaring 100% compatibility with Lua 5.1, let's go to the
  safe ground so.
* Splitted the list in a more granular way.
* Added links to mysql and pg connectors.
* Added queue, vshard, cartridge with links.
* Added a link to the modules page.

Database:

* Replaced MsgPack with MessagePack. It is called so on the official
  website.
* Replaced 'optional persistence' with 'complete WAL-based persistence'
  in the memtx description to make it less confusing. There are users,
  which believe that memtx does not offer persistency.
* Moved SQL down.
* Added JSON path indexes.
* Added synchronous quorum-based replication.
* Added RAFT-based automatic leader election.
* Added a link to the connectors list.

Platforms:

* Dropped OpenBSD from the list. It is not verified in CI, so I feel it
  like 'we have no commitments here'.
* Replaced x86 with more explicit x86_64.
* Moved Mac OS before FreeBSD (we have more users here).
* Added aarch64/M1.

Tarantool is ideal for...

* Kept intact, just reformatted to 80 columns.

Download:

* Added 'or using Docker' in addition to 'as a binary package to your
  OS'.

Added a link to the 'Awesome Tarantool' list.

Report bugs / send feedback or patch:

* Replaced Google Groups with GitHub Discussions.
* Added Stack Overflow.
* Highlighted that we accept pull requests and linked 'How to get
  involved' guide.

Fixes #6579