Make some improvements to the readme (#4998)

This PR fixes some random nits I had with the readme:

* Add badges for python package version, license.
* Use prettier discord badge & put it last.
* Uncapitalize words after the first word in sections, for consistency.
* Rename "in-development" to "unstable" for simplicity & consistency.
* Remove unnecessary paragraph about additional specs.
* Convert sentence about reference tests into bulleted list.
* Use SSH link in cloning instructions.
* Add license to pyproject.toml (to go with our new license badge).

*Note*: The license badge will not work until our next release.

Author: jtraglia

README.md

@@ -1,7 +1,9 @@
 # Ethereum Proof-of-Stake Consensus Specifications
 
-[![Join the chat at https://discord.gg/qGpsxSA](https://img.shields.io/badge/chat-on%20discord-blue.svg)](https://discord.gg/qGpsxSA)
 [![nightly-tests](https://github.com/ethereum/consensus-specs/actions/workflows/nightly-tests.yml/badge.svg?branch=master&event=schedule)](https://github.com/ethereum/consensus-specs/actions/workflows/nightly-tests.yml)
+[![image](https://img.shields.io/pypi/v/eth-consensus-specs.svg)](https://pypi.python.org/pypi/eth-consensus-specs)
+[![image](https://img.shields.io/pypi/l/eth-consensus-specs.svg)](https://pypi.python.org/pypi/eth-consensus-specs)
+[![Discord](https://img.shields.io/badge/Discord-%235865F2.svg?logo=discord&logoColor=white)](https://discord.gg/qGpsxSA)
 
 This repository hosts the current Ethereum
 [proof-of-stake](https://ethereum.org/en/developers/docs/consensus-mechanisms/pos/)
@@ -16,7 +18,7 @@ Core specifications for Ethereum proof-of-stake clients can be found in
 developed in parallel, and then consolidated into sequential upgrades when
 ready.
 
-### Stable Specifications
+### Stable specifications
 
 | Seq. | Code Name     | Fork Epoch | Links                                                                                   |
 | ---- | ------------- | ---------- | --------------------------------------------------------------------------------------- |
@@ -28,7 +30,7 @@ ready.
 | 5    | **Electra**   | `364032`   | [Specs](specs/electra), [Tests](tests/core/pyspec/eth_consensus_specs/test/electra)     |
 | 6    | **Fulu**      | `411392`   | [Specs](specs/fulu), [Tests](tests/core/pyspec/eth_consensus_specs/test/fulu)           |
 
-### In-development Specifications
+### Unstable specifications
 
 | Seq. | Code Name | Fork Epoch | Links                                                                           |
 | ---- | --------- | ---------- | ------------------------------------------------------------------------------- |
@@ -43,20 +45,17 @@ ready.
 
 ### External specifications
 
-Additional specifications and standards outside of requisite client
-functionality can be found in the following repositories:
-
 - [Beacon APIs](https://github.com/ethereum/beacon-apis)
 - [Engine APIs](https://github.com/ethereum/execution-apis/tree/main/src/engine)
 - [Beacon Metrics](https://github.com/ethereum/beacon-metrics)
 - [Builder Specs](https://github.com/ethereum/builder-specs)
 
 ### Reference tests
 
-Stable reference tests are available as
-[release assets](https://github.com/ethereum/consensus-specs/releases) and
-unstable reference tests are available as
-[nightly builds](https://github.com/ethereum/consensus-specs/actions/workflows/nightly-tests.yml).
+- Stable reference tests are available as
+  [release assets](https://github.com/ethereum/consensus-specs/releases).
+- Unstable reference tests are available as
+  [nightly builds](https://github.com/ethereum/consensus-specs/actions/workflows/nightly-tests.yml).
 
 ## Contributors
 
@@ -73,7 +72,7 @@ curl -LsSf https://astral.sh/uv/install.sh | sh
 Clone the repository with:
 
 ```
-git clone https://github.com/ethereum/consensus-specs.git
+git clone git@github.com:ethereum/consensus-specs.git
 ```
 
 Switch to the directory:

pyproject.toml

@@ -6,6 +6,7 @@ name = "eth-consensus-specs"
 dynamic = ["version"]
 authors = [{ name = "ethereum" }]
 description = "Ethereum consensus layer specifications package"
+license = "CC0-1.0"
 readme = { file = "README.md", content-type = "text/markdown" }
 requires-python = ">=3.11, <3.15"
 urls = { homepage = "https://github.com/ethereum/consensus-specs" }