[Python-checkins] devguide: Try to explain the two most common approaches to hg workflow: feature

[Terry Reedy]

> +While non-committers can use named branches without issue, as a core developer
> +you should limit their use to only those branches to be used to collaborate

either /their/your/
or /as a core developer you/core developers/
I prefer latter as parallel to 'non-committers'.