List two more text-only proposals as implemented (#1863)

* List two more text-only proposals as implemented

Update the listing in the README with two more proposals that are
implemented. Also note that they aren't fully standardized at this time
so they're technically subject to change.

* Fix typos

README.md

@@ -187,6 +187,8 @@ Currently implemented proposals in this repository that are stage 4+ are:
   this is an exception, it's not stage4+ but is on-by-default)
 * [x] [exceptions](https://github.com/WebAssembly/exceptions)
 * [x] [extended-const](https://github.com/WebAssembly/extended-const)
+* [x] [extended-name-section](https://github.com/WebAssembly/extended-name-section)
+  (note this is not phase 4 but `wast` does not have the concept of features)
 * [x] [function-references](https://github.com/WebAssembly/function-references)
 * [x] [gc](https://github.com/WebAssembly/gc)
 * [x] [multi-memory](https://github.com/WebAssembly/multi-memory)
@@ -199,6 +201,8 @@ Currently implemented proposals in this repository that are stage 4+ are:
 * [x] [simd](https://github.com/WebAssembly/simd)
 * [x] [tail-call](https://github.com/WebAssembly/tail-call)
 * [x] [threads](https://github.com/WebAssembly/threads)
+* [x] [wat-numeric-values](https://github.com/WebAssembly/wat-numeric-values)
+  (note this is not phase 4 but `wast` does not have the concept of features)
 
 These proposals are implemented but have not yet reached stage 4. This means
 they are disabled by default in validation and their implementation may change