README Usage example nonfunctional

[Preposthumous]

Hi! This is just an issue with the documentation in the main README: The example provided under "Usage" isn't currently functional. Specifically, it includes

chart_default.limits.range_temp_c = (15.0, 35.0)
chart_default.limits.range_humidity_g_kg = (5, 25)

but it appears that the current version of psychrochart doesn't provide a "limits" attribute for a chart object, directly. As far as I can tell, it should read:

chart_default.config.limits.range_temp_c = (15.0, 35.0)
chart_default.config.limits.range_humidity_g_kg = (5, 25)

Thank you for your time and attention!

[azogue]

Thanks for reporting @Preposthumous 👍, fix already included in main branch (from #61)