Update README static asset paths for local Trac setup

[kehach07]

While setting up code.djangoproject.com locally, I noticed that some README commands under the section:

How to port the CSS from djangoproject.com

reference outdated paths that no longer exist.

Current README commands:

cp ../djangoproject.com/static/css/*.css trac-env/htdocs/css/
cp ../djangoproject.com/static/scss/_utils.scss scss/
cp -rT ../djangoproject.com/static/js trac-env/htdocs/js

The correct paths should reference the djangoproject package directory:

cp ../djangoproject.com/djangoproject/static/css/*.css trac-env/htdocs/css/
cp ../djangoproject.com/djangoproject/scss/_utils.scss scss/
cp -rT ../djangoproject.com/djangoproject/static/js trac-env/htdocs/js

Additionally, the SCSS compilation step should mention:

docker compose exec trac make compile-scss
docker compose restart trac

Updating these paths and commands would help contributors complete the local Trac setup successfully and avoid missing CSS/JS assets during development.

[kehach07]

Hi, I opened a PR to update the README paths and Docker SCSS setup instructions for local Trac development:

#300

The changes mainly fix outdated static asset paths and add the correct Docker-based SCSS compilation commands.