Provide more guidance on what makes an issue "easy"

https://github.com/python/devguide/blob/master/triaging.rst#keywords currently states that "easy" issues shouldn't take more than a day for someone new to CPython development, but @gvanrossum pointed out in http://psf.upfronthosting.co.za/roundup/meta/issue605 that that at least needs to be qualified for C level changes based on whether or not the contributor already knows how to program in C.

Guido's specific concern is going to be addressed by splitting the "easy" keyword into "easy (Python)" and "easy (C)", but I think it may be worth providing more concrete guidance to developers and triagers on when it makes sense to mark an issue as "easy". Specifically, I think the main things that make for good first contribution opportunity for folks that aren't sure yet if they want to commit a lot of time are:

• clearly defined scope (specific reproducer for a bug, clear API design for a minor feature)
• already approved-in-principle by a core developer (as this means the issue is likely to have someone willing to review and merge a patch, and is unlikely to get bogged down in debates over whether the bug is actually a bug, or whether the feature addition is a good idea)

Guido also pointed to https://medium.com/@shubheksha/finding-your-first-open-source-project-or-bug-to-work-on-1712f651e5ba#.36q7njkjd as a good overview of the perspective of folks that we're aiming to reach with these "easy" tags.

(To be clear, I'm offering to write a couple of paragraphs for the Triaging page that explains how we seek to use the "easy" keywords, but wanted to discuss our aims for those keywords explicitly before submitting a PR)

從 triaging.rst 的 Keywords 部分開始，檢視現有對 keyword "easy" 的指引。從 contributor 和 triager 的觀點閱讀連結的討論與文章，然後在編輯前確認預期範圍。新增已議定的段落，並釐清應如何使用 keyword "easy (Python)" 和 "easy (C)"，即表示完成。