docs(apify-actor-development): create .actorignore after scaffolding

[DaveHanns]

Rationale

Apify templates (ts_empty, project_empty, python-empty) do not ship a .actorignore file, yet apify push honors one if present. Without it, every push uploads node_modules/, dist/, .git/, and other build caches — bloating uploads and shipping local artifacts that the multi-stage Dockerfile regenerates anyway.

This adds a short subsection under ## Template selection telling the agent to create .actorignore immediately after scaffolding, with a minimal starter set.

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Create .actorignore after scaffolding

Apify templates (including ts_empty, project_empty, python-empty) do not include a .actorignore file, even though apify push honors one if present. Without it, every apify push uploads node_modules/, dist/, build caches, .git/, and anything else in the working tree — bloating the upload and shipping local build artifacts the multi-stage Dockerfile regenerates anyway.

Create .actorignore at the project root with at minimum:

node_modules
dist
.git
.env*
*.log
coverage
.DS_Store

Syntax is .gitignore-style.

Surfaced during an evaluation of Apify surfaces for agent-driven Actor development.