docs: correct the claims that no longer match the code

- the custom model option does not exist for every provider; name any model ID instead
- alpha is measured against the regional benchmark, not always SPY
- the environment overrides a fixed set of config keys
- list the providers the picker offers, and the macro data key
- drop the example call to a method that was removed

main.py

@@ -16,4 +16,3 @@ _, decision = ta.propagate("NVDA", "2026-09-01")
 print(decision)
 
 # Memorize mistakes and reflect
-# ta.reflect_and_remember(1000) # parameter is the position returns