message: Fix link to language sections
  Fixes
diff: @@ -67,7 +67,7 @@ An Instruction represents a unit of computational work.
  Every instruction must have this field:
  * `op`, a string: the *opcode* that determines what the instruction does.
  - (See the [*Operations*](#operations) section, below.)
  + (See the [*Core Language*](core.md) section and the subsequent extension sections for listings of the available opcodes.)
  Depending on the opcode, the instruction might also have:
  