Help to set expectations for issues up front (#4513)

.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +1,5 @@
 blank_issues_enabled: false
 contact_links:
-  - name: Open a Discussion
+  - name: Propose a language idea or ask a question
     url: https://github.com/dotnet/csharplang/discussions/new
-    about: Please open new proposals as discussions if they are not fully specified.
+    about: Starting with discussion is the way to create a new proposal.

.github/ISSUE_TEMPLATE/proposal_template.md

@@ -1,10 +1,12 @@
 ---
-name: Language Proposal
-about: Fully specified language proposal
+name: Create a language specification
+about: For proposals that have been invited by a team member.
 title: "[Proposal]: [FEATURE_NAME]"
 ---
 <!--
-New language feature proposals should fully fill out this template. This should include a complete detailed design, which describes the syntax of the feature, what that syntax means, and how it affects current parts of the spec. Please make sure to point out specific spec sections that need to be updated for this feature. If you do not have the knowledge or experience to fill this out completely, that's perfectly alright: please open this proposal as a Discussion instead (https://github.com/dotnet/csharplang/discussions/new) and the community can generally discuss the proposal in less formal terms.
+Hello, and thanks for your interest in contributing to C#! If you haven't been invited by a team member to open an issue, please instead open a discussion marked [draft issue] at https://github.com/dotnet/csharplang/discussions/new and we'll try to give you feedback on how to get to an issue-ready proposal.
+
+New language feature proposals should fully fill out this template. This should include a complete detailed design, which describes the syntax of the feature, what that syntax means, and how it affects current parts of the spec. Please make sure to point out specific spec sections that need to be updated for this feature.
 -->
 # FEATURE_NAME