docs: improve consistency across documentation

[sashaodessa]

This PR fixes typos, grammatical errors, and improves consistency across all documentation files in the repository.

README.md

• Improved wording: "implementation of a Reth Ethereum node" → "Reth-based Ethereum node implementation"
• Fixed grammar: "Built upon Reth, see version" → "Built upon Reth. See the version"
• Added missing article: "see version pinned" → "see the version pinned"

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1