Update planning.md

doc/planning.md

@@ -40,10 +40,10 @@ UVM has been [designed](/doc/design.md) with JIT compilation in mind, that
 is, we've made multiple design choices that we think will make it easier
 to generate efficient machine code from our bytecode instructions. We
 believe it should be possible to get good performance with a fairly
-simple JIT compiler. A speedup of 20x or more over the interpreter
-should be expected, and hopefully near-native performance.
+simple JIT compiler. A speedup of ~20x over the interpreter
+should be achievable, and hopefully near-native performance.
 
-We don't want to stat working on the JIT compiler very early in the
+We don't want to start working on the JIT compiler very early in the
 prototype stage, because it's easier to quickly iterate over the design
 while working with an interpreter, but experimentation with
 JIT compilation needs to happen before we stabilize the current design.