Clarify API in readme (#27)

Closes #26

Author: timholy

README.md

@@ -2,8 +2,8 @@
 
 This package performs operations on Julia's [lowered AST](https://docs.julialang.org/en/latest/devdocs/ast/).
 Current utilities include:
-- `signature`: compute the signature of a specific method
-- `methoddef!`: extract a method signature from lowered code
+- `signature`: compute the signature of a single method from its lowered definition
+- `methoddef!`: find signatures and optionally evaluate methods from lowered code
 - `rename_framemethods!`, resolve gensymmed names (https://github.com/JuliaLang/julia/issues/30908)
 - `bodymethod`: find the method that executes the body of a keyword-argument function