Mark Observables proposal as ready to advance

Reference tc39/agendas@b447caf
cc @jhusain

README.md

@@ -32,7 +32,7 @@ Proposals follow [this process document](https://tc39.github.io/process-document
 |   | [Date.parse fallback semantics](https://github.com/mrrrgn/proposal-date-time-string-format)               | Morgan Phillips                    | 1 |
 |   | [`export * as ns from "mod";` statements](https://github.com/leebyron/ecmascript-export-ns-from)          | Lee Byron                          | 1 |
 |   | [`export v from "mod";` statements](https://github.com/leebyron/ecmascript-export-default-from)           | Lee Byron                          | 1 |
-|   | [Observable](https://github.com/tc39/proposal-observable)                                                 | Jafar Husain and Mark Miller       | 1 |
+| 🚀 | [Observable](https://github.com/tc39/proposal-observable)                                                 | Jafar Husain and Mark Miller       | 1 |
 |   | [String#matchAll](https://github.com/tc39/String.prototype.matchAll)                                      | Jordan Harband                     | 1 |
 |   | [WeakRefs](https://github.com/tc39/proposal-weakrefs)                                                     | Dean Tribble                       | 1 |
 |   | [Frozen Realms](https://github.com/FUDCo/frozen-realms)                                      | Mark S. Miller, Chip Morningstar, Caridy Patiño | 1 |