docs: fix contributor docs links and typos (#18637)

## Summary

This PR fixes several small documentation issues in the contributor and
setup guides:

- fixes broken docs links in the root README
- corrects multiple typos and capitalization issues in contributor docs
- fixes malformed Markdown for the Redis command in local setup
- improves wording in the Docker Compose self-hosting guide

## Changes

- updated README installation links to the current docs routes
- changed `Open-source` to `open-source`
- fixed `specially` -> `especially` in the frontend style guide
- normalized `MacOS` -> `macOS`, `powershell` -> `PowerShell`, and
`Postgresql` -> `PostgreSQL`
- replaced the invalid `localhost:5432` Markdown link with inline code
- fixed the malformed fenced code block for `brew services start redis`
- cleaned up Redis naming/capitalization and a few grammar issues in the
setup docs
- improved the warning and environment-variable wording in the Docker
Compose guide

## Testing

- not run; docs-only changes

---------

Co-authored-by: Charles Bochet <charlesBochet@users.noreply.github.com>

packages/twenty-docs/developers/self-host/capabilities/docker-compose.mdx

@@ -4,7 +4,7 @@ title: 1-Click w/ Docker Compose
 
 
 <Warning>
-Docker containers are for production hosting or self-hosting, for the contribution please check the [Local Setup](/developers/contribute/capabilities/local-setup).
+Docker containers are for production hosting or self-hosting. For contributing, please check the [Local Setup](/developers/contribute/capabilities/local-setup).
 </Warning>
 
 ## Overview
@@ -13,7 +13,7 @@ This guide provides step-by-step instructions to install and configure the Twent
 
 **Important:** Only modify settings explicitly mentioned in this guide. Altering other configurations may lead to issues.
 
-See docs [Setup Environment Variables](/developers/self-host/capabilities/setup) for advanced configuration. All environment variables must be declared in the docker-compose.yml file at the server and / or worker level depending on the variable.
+See [Setup Environment Variables](/developers/self-host/capabilities/setup) for advanced configuration. All environment variables must be declared in the `docker-compose.yml` file at the server and/or worker level, depending on the variable.
 
 ## System Requirements
 
@@ -237,4 +237,3 @@ docker compose up -d
 
 If you encounter any problem, check [Troubleshooting](/developers/self-host/capabilities/troubleshooting) for solutions.
 
-