Few README.md updates

[MMilosz]

References

None

Description

Few maintenance updates to README documentation. Changes reflected in commit history.

Note: the README would benefit from a more thorough re-visit

Changes

• Updated ToC (removed nonexisting #deploy, renamed #collaborating -> #contributing, added missing headers)
• Unit/E2E Tests section: replaced npm run coverage (it does not exist) with npm run test:headless and npm run test:watch, updated Cypress extension .spec.ts -> .cy.ts
• Other commands section: removed paragraph about pre or post scripts (pree2e, prebuild etc. were used before 2021, see: 71f5b46), added info on npm run & npm run <script-name>
• File Tree section: added some relevant files, fixed some entries
• Editor/IDE section: removed deprecated 'Debugger for Chrome' (it's now built natively into VS Code)
• FAQ section: removed 'node-pre-gyp ERR in npm install' (python 2 has been deprecated for years, also the official Node.js for Windows installer now automatically installs the required tools)
• Converted Docker production warning to Markdown Alert format for visibility
• Some typos corrections, minor grammar changes, http->https, URL updates, etc.

Instructions for Reviewers

No functional changes. Review changes in README.md

Checklist

Note: I've checked all items in the checklist as this is a documentation-only update, so code-related items do not apply.

• My PR is created against the main branch of code (unless it is a backport or is fixing an issue specific to an older branch).
• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR follows all coding best practices based on the Code Conventions Guide
• My PR passes ESLint validation using npm run lint
• My PR doesn't introduce circular dependencies (verified via npm run check-circ-deps)
• My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• My PR aligns with Accessibility guidelines if it makes changes to the user interface.
• My PR uses i18n (internationalization) keys instead of hardcoded English text, to allow for translations.
• My PR includes details on how to test it. I've provided clear instructions to reviewers on how to successfully test this fix or feature.
• If my PR includes new libraries/dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.
• If my PR includes new features or configurations, I've provided basic technical documentation in the PR itself.
• If my PR fixes an issue ticket, I've linked them together.