docs(readme): add onboarding steps for PROVABLY_API_KEY + PROVABLY_ORG_ID

New 'Getting PROVABLY_API_KEY and PROVABLY_ORG_ID' subsection under Configuration:

  1. Sign up at app.provably.ai
  2. Create an organisation (org id shown in the URL)
  3. Left-side menu → Integrations → create one (generated key)

Plus a pointer to provably.ai/docs for full product documentation.

Closes the gap surfaced while users were trying to find where these values come
from — the env-var table told them they were required but not where to source them.

Author: aural-psynapse

README.md

@@ -160,6 +160,14 @@ The SDK reads configuration from environment variables. A typed
 `Provably(api_key=..., org_id=..., ...)` client that replaces these globals is
 planned (issue [#2](https://github.com/ProvablyAI/provably-python-sdk/issues/2)).
 
+#### Getting `PROVABLY_API_KEY` and `PROVABLY_ORG_ID`
+
+1. Sign up at [app.provably.ai](https://app.provably.ai).
+2. Create an organisation. The org id is shown in the URL after creation and is what goes in `PROVABLY_ORG_ID`.
+3. In the left-side menu, go to **Integrations** and create one. The generated key is your `PROVABLY_API_KEY`.
+
+Full product docs: [provably.ai/docs](https://provably.ai/docs).
+
 | Variable | Used by | Required |
 |---|---|---|
 | `PROVABLY_API_KEY` | `initialize_runtime`, integration cache | yes |