Update `idris-make-lemma` to insert lemma above doc string of current function.

[keram]

Why: Previously if function had a doc string the lemma was inserted before signature but after the doc string requiring user to further adjust the position.

Before:

||| Useful doc for foo
foo_rhs : String -> String

foo : String -> String
foo str = foo_rhs str

After:

foo_rhs : String -> String

||| Useful doc for foo
foo : String -> String
foo str = foo_rhs str