Add BIOS and tiny kernel roadmap phases

Tutorial/phase-10-elf-loader/phase-10.md

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+# Phase 10 - Minimal ELF Loader
+
+## Context
+
+This phase lets the BIOS receive GCC-built programs as ELF files and run them without
+rebuilding the FPGA bitstream.
+
+## Goals
+
+- Parse enough ELF32 to recognize RISC-V executable files.
+- Load `PT_LOAD` segments into memory and zero BSS.
+- Jump to `e_entry` with a fixed tiny-program ABI.
+
+## New Concepts
+
+- ELF header: file-level metadata describing architecture, entry point, and tables.
+- Program header: runtime load description used by loaders.
+- `PT_LOAD`: segment that must be copied into memory before execution.
+- BSS: zero-initialized memory represented by `memsz > filesz`.
+
+## How To Think About It
+
+Do not build a general-purpose dynamic loader. Build a strict loader for the exact
+firmware shape you produce: static, little-endian, non-relocatable RV32 ELF files with
+fixed physical addresses.
+
+## Learning Tasks
+
+- Read the ELF header fields needed to reject unsupported files.
+- Map `p_paddr` or `p_vaddr` to your executable memory window.
+- Define the stack pointer and argument registers at program entry.
+- Decide how a loaded program returns a status code to the BIOS.
+
+## Pitfalls
+
+- Trusting malformed ELF offsets or sizes.
+- Forgetting to zero the BSS tail of a loadable segment.
+- Accidentally accepting relocatable or dynamically linked binaries.
+- Loading a segment over the BIOS itself.
+
+## Tooling And Testing
+
+- Use `readelf -h -l` and `objdump -d` on every early payload.
+- Start with one fixed link address and one loadable segment.
+- Add loud rejection messages for unsupported ELF class, endianness, machine, or type.
+
+## References
+
+- ELF specification overview: https://refspecs.linuxfoundation.org/elf/elf.pdf
+- RISC-V ELF psABI: https://github.com/riscv-non-isa/riscv-elf-psabi-doc
+- GNU binutils `readelf` documentation: https://sourceware.org/binutils/docs/binutils/readelf.html