README: document mame-tecmo and mame-technos delivery branches

[arena-ai-coding-agent]

Documents the mame-tecmo and mame-technos orphan branches (and the rest of the manufacturer set) in the repo README, so agents can find and use the prebuilt headless MAME binaries.

What's on the new branches

Branch	Build	Compressed binary	Spot-check
mame-tecmo	Headless MAME v0.289, OSD=headless SOURCES=src/mame/tecmo	mame.xz ~10 MB (75 MB raw)	./mame -listfull rygar → Rygar (US set 1)
mame-technos	Headless MAME v0.289, OSD=headless SOURCES=src/mame/technos	mame.xz ~11 MB (75 MB raw)	./mame -listfull ddragon → Double Dragon (World set 1)

Each branch also ships mcp-server, plugins/mcp, the artwork/roms/samples data dirs, and the manufacturer driver sources as reference. ldd is libc/libstdc++/libm/libgcc only.

Together with the existing mame-konami, mame-capcom, mame-sega and mame-taito branches, the manufacturer set is complete.

What this PR adds to the README

• A branches table covering every mame-<system> delivery branch.
• How to decompress and run a binary, plus the MCP client config snippet.
• The exact headless build/package steps used to produce these artifacts (from Parisoft/mame-mcp).

Verification

$ xz -dk mame.xz && chmod +x mame
$ ldd mame          # libc, libstdc++, libm, libgcc only
$ ./mame -help      # MAME v0.289, works with no DISPLAY
$ ./mame -listfull rygar     # tecmo
$ ./mame -listfull ddragon   # technos

Note: this PR only touches README.md. The binaries live on the mame-tecmo / mame-technos orphan branches, so main history stays clean — merge this and main is unchanged apart from the docs.