Windows: product names, the editors, WSL; the Linux page's image step

Assembled from development commit c3c40f6c8fca. Since 830b193: on Windows the
products carry Windows names (ktext.exe, klammertext.dll, document.dll,
reflect.dll) and the console's output code page is UTF-8 for a run; the
editor tooling works on Windows (VS Code, Sublime Text, Vim, with the
interpreter's name chosen by platform) and Notepad++ joins it
(doc/edit/notepadpp: a User Defined Language and two Run-menu commands);
a sixth install page, doc/install/windows_wsl_install.md, for Linux
inside WSL; the Windows page opens with the three routes and gains its
editor section, the PowerShell quoting and Path notes; the Linux page
installs OpenImageIO from the python3-openimageio package and verifies
with kdiag --machine; the README lists all six install pages. Linux and
macOS behaviour is unchanged.

doc/edit/vscode/README.md

@@ -18,8 +18,9 @@ language's structure, everywhere.
 - VS Code 1.75 or later — a minimum, not a target: VS Code's monthly
   releases count 1.75, 1.76, … (1.75 is from January 2023), so any
   version from the last few years qualifies.
-- `python3` on `PATH` (or set `klammertext.pythonPath`); Klammertext itself
-  already requires Python.
+- `python3` on `PATH` — on Windows `python`, the name python.org installs
+  (or set `klammertext.pythonPath`); Klammertext itself already requires
+  Python.
 - The language server, found automatically in this order:
   1. the `klammertext.serverPath` setting, if set;
   2. `klammertext_ls.py` vendored next to `extension.js` (the layout the
@@ -32,8 +33,9 @@ language's structure, everywhere.
 ## Install
 
 Package the extension as a `.vsix` and install it (the builder needs only
-bash and python3; the editing zip from the Klammertext website ships a
-prebuilt `klammertext.vsix`, so there the first step is already done):
+bash and Python — on Windows, run it in the MSYS2 shell the Klammertext
+build uses; the editing zip from the Klammertext website ships a prebuilt
+`klammertext.vsix`, so there the first step is already done):
 
     ./make_vsix.sh
     code --install-extension klammertext.vsix
@@ -129,7 +131,7 @@ Shortcuts** (`Ctrl+K Ctrl+S`), search "klammertext", and rebind.
 ## Settings
 
 A normal installation needs neither setting: the extension runs `python3`
-from `PATH` and finds the language server automatically (the copy vendored
+(on Windows `python`) from `PATH` and finds the language server automatically (the copy vendored
 next to `extension.js`, then `../shared/`, then
 `$KLAMMERTEXT_HOME/doc/edit/shared/`).  They exist for unusual setups.
 Set them in the Settings UI (`Ctrl+,`, search "klammertext") or in
@@ -138,10 +140,10 @@ reload the window after changing either.
 
 | Setting | Meaning (default) |
 |---|---|
-| `klammertext.pythonPath` | Python interpreter for the server (`python3`) |
+| `klammertext.pythonPath` | Python interpreter for the server (`python3`; on Windows `python`) |
 | `klammertext.serverPath` | full path to `klammertext_ls.py` (auto-located) |
 
-`pythonPath` matters when `python3` is not on the `PATH` VS Code sees — a
+`pythonPath` matters when the interpreter is not on the `PATH` VS Code sees — a
 VS Code launched from the desktop inherits a different environment than
 your shell — or when a specific interpreter is wanted.  `serverPath`
 matters only when the server file lives outside the search chain above.