Fix bitstring order in precise GC docs (#3947)

docs: Fix bitstring order in precise GC docs

src/runtime/gc_precise.go

@@ -18,8 +18,8 @@
 // | object type | size | bitstring | note
 // |-------------|------|-----------|------
 // | int         | 1    |   0       | no pointers in this object
-// | string      | 2    | 10        | {pointer, len} pair so there is one pointer
-// | []int       | 3    | 100       | {pointer, len, cap}
+// | string      | 2    |  01       | {pointer, len} pair so there is one pointer
+// | []int       | 3    | 001       | {pointer, len, cap}
 // | [4]*int     | 1    |   1       | even though it contains 4 pointers, an array repeats so it can be stored with size=1
 // | [30]byte    | 1    |   0       | there are no pointers so the layout is very simple
 //