Add weather lookup function example

[Thomasyoung113]

Adds a new weather lookup function using wttr.in API as an example for function calling.

Changes

• Added get_weather() function to functions.py that fetches current weather data from wttr.in API
• Returns temperature, humidity, wind speed, conditions and more
• Updated README.md with documentation of all available functions including the new weather function
• Added example usage showing how to query weather for any location

Example

python functioncall.py --query "What's the weather like in Tokyo?"