[Propeller][ELF] Add Doxygen comment for decodeBBAddrMap

[aidengrossman]

Summary

Pretty minor change, but I figured it would be nice to have some documentationon decodeBBAddrMap easily available in the header/doxygen for whenever someone needs to read through it/code calling it.

llvm/include/llvm/Object/ELF.h

public:
   getSectionName(const Elf_Shdr &Section,
                  WarningHandler WarnHandler = &defaultWarningHandler) const;
   Expected<StringRef> getSectionName(const Elf_Shdr &Section,
                                      StringRef DotShstrtab) const;
   template <typename T>
   Expected<ArrayRef<T>> getSectionContentsAsArray(const Elf_Shdr &Sec) const;
   Expected<ArrayRef<uint8_t>> getSectionContents(const Elf_Shdr &Sec) const;
   Expected<ArrayRef<uint8_t>> getSegmentContents(const Elf_Phdr &Phdr) const;
+
+  /// Returns a vector of BBAddrMap structs corresponding to each function
+  /// within the text section that the SHT_LLVM_BB_ADDR_MAP section \p Sec
+  /// is associated with. If the current ELFFile is relocatable, a corresponding
+  /// \p RelaSec must be passed in as an argument.
   Expected<std::vector<BBAddrMap>>
   decodeBBAddrMap(const Elf_Shdr &Sec, const Elf_Shdr *RelaSec = nullptr) const;
 
   /// Returns a map from every section matching \p IsMatch to its relocation
   /// section, or \p nullptr if it has no relocation section. This function
   /// returns an error if any of the \p IsMatch calls fail or if it fails to
   /// retrieve the content section of any relocation section.
   Expected<MapVector<const Elf_Shdr *, const Elf_Shdr *>>