docs: the Windows build is a cross-compile, and only that

The docs offered a native build as an equal alternative -- "the same
command builds natively on the Windows box itself, with zig on PATH and
a make" -- and it does not work. Makefile.windows needs sed, cat,
mkdir -p and shell grouping, none of which cmd.exe has; and on ARM64
`zig cc` in zig 0.16.0 dies with an access violation on a one-line C
file, so the compiler cannot run there at all. The zip that does it
matches the published shasum, so this is upstream rather than a bad
download.

Nobody following those two sentences reached a binary. So they are
gone, along with the "# host arch, native" usage line in the makefile
and the "cross-compiles too" aside in the two install sections, which
both implied that building on the box was the normal path and the
cross-compile a bonus. It is the other way round, and now the pages
say so once, in the same words each time.

`builds and runs natively` on the doc's first line loses `builds`:
what is native about slosh.exe is the binary, not where it was made.

2 files changed, 13 insertions, 10 deletions

diff --git a/docs/index.md b/docs/index.md
index d7513dc..ad90c7f 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -37,8 +37,10 @@ there.)
 Windows 10/11, x86-64 and ARM64, as one `slosh.exe`. Panes are ConPTYs and
 sessions are AF_UNIX sockets, so everything documented here works there too.
 
+Cross-compiled from a mac or a Linux box, then copied across:
+
 ```bash
-make -f Makefile.windows ARCH=x86_64    # or ARCH=aarch64; cross-compiles too
+make -f Makefile.windows ARCH=x86_64    # or ARCH=aarch64
 ```
 
 The details, and the three decisions the port rests on: [windows](windows.md).
diff --git a/docs/windows.md b/docs/windows.md
index 12b4a8c..861a3cd 100644
--- a/docs/windows.md
+++ b/docs/windows.md
@@ -1,20 +1,21 @@
 # Windows
 
-slosh builds and runs natively on Windows 10/11, on both x86-64 and ARM64. It
-is one `slosh.exe` with no runtime dependency beyond the OS.
+slosh runs natively on Windows 10/11, on both x86-64 and ARM64. It is one
+`slosh.exe` with no runtime dependency beyond the OS.
+
+The build is a cross-compile, from a mac or a Linux box:
 
 ```bash
-make -f Makefile.windows ARCH=x86_64     # cross-compile from mac or Linux
+make -f Makefile.windows ARCH=x86_64
 make -f Makefile.windows ARCH=aarch64
 ```
 
-`ARCH` defaults to `aarch64`. The same command builds natively on the Windows
-box itself, with zig on `PATH` and a `make`. The vendored terminal core is
-cross-compiled the same way and lands in
-`vendor/libghostty-vt/zig-out-win-<arch>`, so the two architectures never share
-an output directory.
+`ARCH` defaults to `aarch64`. The vendored terminal core is cross-compiled the
+same way and lands in `vendor/libghostty-vt/zig-out-win-<arch>`, so the two
+architectures never share an output directory.
 
-The binary appears at `build/win-<arch>/slosh.exe`.
+The binary appears at `build/win-<arch>/slosh.exe`; copy that to the Windows
+machine.
 
 ## What it does there