Add conditional-sections as an inactive proposal

inactive-proposals.md

@@ -5,8 +5,11 @@ Inactive proposals are proposals that at one point were presented to the communi
 | Proposal                                 | Champion         | Rationale                                                              |
 | ---------------------------------------- | ---------------- | ---------------------------------------------------------------------- |
 | [Unmanaged closures][unmanaged_closures] | Mark Miller      | Withdrawn in favor of [Typed Function References][function_references] |
+| [Conditional sections][cond_sections]    | Thomas Lively    | Withdrawn in favor of [Feature detection][feature_detection]           |
 
 See also the [active proposals](README.md) and [finished proposals](finished-proposals.md) documents.
 
 [unmanaged_closures]: https://github.com/WebAssembly/proposals/issues/6
 [function_references]: https://github.com/WebAssembly/function-references
+[cond_sections]: https://github.com/WebAssembly/conditional-sections
+[feature_detection]: https://github.com/WebAssembly/feature-detection