- Update README and add more docstrings and comments in code

[dmzolotarev]

This is Junie-generated additions to project documentations, pls proof-read them before merging, they might have redundant/incorrect information

[kosstbarz]

Let's replace all this with simple
pip install portus-ai

[kosstbarz]

Let's use instead

import portus
config = portus.LLMConfig(name="gpt-4o-mini", temperature=0)
session = portus.open_session(...)

[kosstbarz]

I think we should not give advices in the doc.
We can just show how we read secrets from the env:

user = os.environ.get("DATABASE_USER")
...
url = f"postgresql://{user}:{password}@{host}/{database}"

[kosstbarz]

While we use not uv but pip install, there should be another way to specify keys.
Probably we can say:

Specify your API keys in the env vars:
- `OPENAI_API_KEY` — if using OpenAI models
- `ANTHROPIC_API_KEY` — if using Anthropic models
- Optional for local/OAI‑compatible servers:
  - `OPENAI_BASE_URL` (aka `api_base_url` in code)
  - `OLLAMA_HOST` (e.g., `127.0.0.1:11434`)

[mare5x]

portus to databao 😃 😇