Improve guidance about proposals (swiftlang#932)

Author: ktoso

gsoc2025/index.md

@@ -28,6 +28,8 @@ Getting familiar with the codebase you are interested in working on during GSoC
 
 When it comes to writing the proposal, the [Google Summer of Code Guide](https://google.github.io/gsocguides/student/writing-a-proposal) contains general, good advice.
 
+The best proposals include a detailed timeline, specific milestones and goals as well as an outline the technical challenges you foresee. It is best if you engage with your potential project mentor on the forums before contriburing, and have them clarify the goals and steps that they think are necessary for the project to be successful. Your proposal should have a clear goal, which can be successfully achieved as part of the weeks you'll be working it. Provide details about your approach, significant milestones you wish to achieve, and clarify with your potential mentor if they agree those seem reasonable. The time before proposal submissions is there for you to reach out and polish your proposal, so make sure you use it well! Good luck!
+
 ## Potential Projects
 
 We are currently collecting project ideas on the forums in the dedicated [GSoC category](https://forums.swift.org/c/development/gsoc/98).