Move external links to separate See Also section

Split Related Projects into sibling project cross-references
and a See Also section for external resources.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Aaron Wohl

README.md

@@ -178,6 +178,9 @@ upeepz80 is a sibling project to upeep80, designed for compilers that generate n
 - [um80_and_friends](https://github.com/avwohl/um80_and_friends) - Microsoft MACRO-80 compatible toolchain for Linux: assembler, linker, librarian, disassembler
 - [uplm80](https://github.com/avwohl/uplm80) - PL/M-80 compiler targeting Intel 8080 and Zilog Z80 assembly language
 - [z80cpmw](https://github.com/avwohl/z80cpmw) - Z80 CP/M emulator for Windows (RomWBW)
+
+## See Also
+
 - [upeep80](https://github.com/avwohl/upeep80) - Optimizer with 8080 input support
 - [Z80 CPU User Manual](http://www.z80.info/zip/z80cpu_um.pdf)