add sig files for section and strtab section

Author: katsyoshi

sig/caotral/linker/elf/section.rbs

@@ -0,0 +1,8 @@
+class Caotral::Linker::ELF::Section
+  attr_accessor header: untyped
+  attr_accessor body: untyped
+  attr_accessor section_name: String
+
+  def initialize: (type: Symbol, ?section_name: String?, ?options: Hash[Symbol, untyped]) -> void
+  def name: () -> String
+end

sig/caotral/linker/elf/section/strtab.rbs

@@ -0,0 +1,8 @@
+class Caotral::Linker::ELF::Section::Strtab
+  attr_reader names: String
+
+  def initialize: (?String, **untyped) -> void
+  def build: () -> String
+  def offset_of: (String) -> Integer?
+  def lookup: (Integer) -> String
+end