docs: answer the installer questions on the page

wiki/faq.md

@@ -92,6 +92,48 @@ python scripts/verify.py --emulator beetle_psx --verbose
 
 The `--verbose` flag shows source references and expected values from the emulator's source code.
 
+## Is piping the installer into a shell safe?
+
+The one-liner runs a small bootstrap, not the installer. That bootstrap fetches
+`install.py` over HTTPS only, refuses anything over 2 MB, and requires its
+SHA-256 to equal the value written inside the bootstrap itself. A substituted
+installer aborts with `install.py SHA-256 mismatch` before a single line of it
+runs.
+
+The installer then verifies every file it downloads against the size, SHA-256
+and SHA-1 the manifest declares, and moves it into place only once those match.
+The manifest is treated as untrusted: a destination cannot be absolute, carry a
+drive letter or climb out of the BIOS directory.
+
+Reading the bootstrap before running it is two lines:
+
+```bash
+curl -fsSL https://raw.githubusercontent.com/Abdess/retrobios/main/install.sh -o install.sh
+less install.sh && sh install.sh
+```
+
+See [Installer](installer.md) for the full behaviour.
+
+## Can I run the installer again?
+
+Yes, and re-running is the normal way to update. A file already present with
+the expected hash is left untouched, one whose contents do not match is
+replaced by the verified copy, and files the manifest does not name are never
+read, moved or deleted. `--check` does the same inspection and exits without
+writing.
+
+## Can I install onto an SD card or another machine's drive?
+
+Yes, `--dest` takes any path and the one-liner forwards arguments:
+
+```bash
+curl -fsSL https://raw.githubusercontent.com/Abdess/retrobios/main/install.sh \
+  | sh -s -- --platform retroarch --dest /path/to/sdcard
+```
+
+On Windows the arguments need a script block, since `iex` would read them as
+its own; the form is on the [Installer](installer.md#passing-options) page.
+
 ## Is this legal?
 
 Redistributing firmware is not settled law, and this page does not pretend otherwise. What follows is the reasoning the project acts on, with the strength of each argument stated plainly so anyone can weigh it. None of it is legal advice, and none of it has been tested in court.

wiki/installer.md

@@ -110,6 +110,7 @@ Checking existing files...
 | `--jobs N`, `-j N` | Parallel downloads, 1 to 32, default 8 |
 | `--verbose`, `-v` | Print per-attempt failures and hash mismatches |
 | `--standalone-copies` | Also copy into detected standalone emulator directories |
+| `--help`, `-h` | Print the option list and exit |
 
 `--check` reads the same file list, hashes the destination and exits. Without
 it, a file already present with the expected hash is left untouched, and one
@@ -125,7 +126,7 @@ Files the list does not name are never read, moved or deleted.
 | `RETROBIOS_OS` | Names the host outright (`linux`, `wsl`, `windows`, `darwin`) instead of detecting it |
 | `RETROBIOS_INSTALL_URL` | Where the bootstrap fetches `install.py`. HTTPS only |
 | `RETROBIOS_INSTALL_SHA256` | The SHA-256 the bootstrap requires of that installer, 64 hex characters |
-| `HTTPS_PROXY` | Honoured for every download, through the standard library's default proxy handling |
+| `HTTPS_PROXY`, `NO_PROXY` | Honoured for every download through the standard library's default proxy handling: one names the proxy, the other the hosts to reach directly |
 
 ## Platform detection
 
@@ -183,6 +184,46 @@ With nothing detected, the installer lists the platforms and asks. With several
 detected, it asks which one. Both prompts need a terminal: piped into a script
 with no platform to install for, it prints the manual invocation and exits 1.
 
+## Standalone copies
+
+Some files are read by a standalone emulator from its own data directory
+rather than from the platform's BIOS tree. `--standalone-copies` copies them
+there after the install, and only then: without the flag nothing is written
+outside the selected tree.
+
+The manifest carries the list, fifteen entries on the six platforms that
+declare them (Batocera, EmuDeck, Recalbox, RetroArch, RetroBat, RetroDECK):
+
+| Files | Copied to |
+|-------|-----------|
+| `prod.keys`, `title.keys` | yuzu, eden, citron, suyu and Ryujinx key directories |
+| `Citra/sysdata/aes_keys.txt`, `Citra/sysdata/boot9.bin` | Azahar `sysdata` |
+| `scph*.bin` | DuckStation `bios` |
+| `ps2-*.bin` | PCSX2 `bios`, native and Flatpak |
+| `GC/USA/IPL.bin`, `GC/EUR/IPL.bin`, `GC/JAP/IPL.bin`, `dsp_rom.bin`, `dsp_coef.bin` | Dolphin, per region for the IPL |
+| `PPSSPP/ppge_atlas.zim` | PPSSPP `PSP/SYSTEM` |
+| `dc/dc_boot.bin`, `dc/dc_nvmem.bin` | Flycast `data`, native and Flatpak |
+
+An entry names one file or a glob, and one entry carries no file at all: when
+an RPCS3 configuration directory is present it prints that `PS3UPDAT.PUP` is
+installed through RPCS3's own File menu, since that firmware is an installer to
+run rather than a file to copy.
+
+Targets are per OS, WSL falling back to the Linux ones. A directory that does
+not exist is skipped rather than created, so nothing is copied for an emulator
+that is not installed. A destination that is already a symbolic link is skipped
+too: the copy leaves the tree the user opted into, and a link there would
+redirect the write somewhere else again.
+
+## Android
+
+There is no Android detection. Termux reports itself as Linux, so nothing is
+found and the platform has to be named along with where it writes:
+
+```bash
+python install.py --platform retroarch --dest /storage/emulated/0/RetroArch/system
+```
+
 ## Where the files come from
 
 Each manifest entry names either `repo_path`, served from the repository at the