configs: use Notepad as default editor on Windows

CHANGELOG.md

···
 
 * The `push.branch-prefix` option was renamed to `git.push-branch-prefix`.
 
+* The default editor on Windows is now `Notepad` instead of `pico`.
+
 ### New features
 
 * `jj init --git-repo` now works with bare repositories.

cli/src/commands/mod.rs

···
 /// Update the change description or other metadata
 ///
 /// Starts an editor to let you edit the description of a change. The editor
-/// will be $EDITOR, or `pico` if that's not defined.
+/// will be $EDITOR, or `pico` if that's not defined (`Notepad` on Windows).
 #[derive(clap::Args, Clone, Debug)]
 struct DescribeArgs {
     /// The revision whose description to edit

cli/src/config.rs

···
             config::File::from_str(include_str!($file), config::FileFormat::Toml)
         };
     }
-    config::Config::builder()
+    let mut builder = config::Config::builder()
         .add_source(from_toml!("config/colors.toml"))
         .add_source(from_toml!("config/merge_tools.toml"))
         .add_source(from_toml!("config/misc.toml"))
-        .add_source(from_toml!("config/templates.toml"))
-        .build()
-        .unwrap()
+        .add_source(from_toml!("config/templates.toml"));
+    if cfg!(unix) {
+        builder = builder.add_source(from_toml!("config/unix.toml"))
+    }
+    if cfg!(windows) {
+        builder = builder.add_source(from_toml!("config/windows.toml"))
+    }
+    builder.build().unwrap()
 }
 
 /// Environment variables that override config values

cli/src/config/misc.toml

···
 # Placeholder: added by user
 
 [ui]
-editor = "pico"
 pager = { command = ["less", "-FRX"], env = { LESSCHARSET = "utf-8" } }
 log-word-wrap = false

cli/src/config/unix.toml

···
+[ui]
+editor = "pico"

cli/src/config/windows.toml

···
+[ui]
+editor = "Notepad"

docs/config.md

···
 
 `$JJ_EDITOR` > `ui.editor` > `$VISUAL` > `$EDITOR`
 
-Pico is the default editor in the absence of any other setting, but you could
-set it explicitly too.
+Pico is the default editor (Notepad on Windows) in the absence of any other
+setting, but you could set it explicitly too.
 
 ```toml
 ui.editor = "pico"

docs/config.toml

···
 ui.color = "auto" # the default
 # ui.color = never # no color
 
-ui.editor = "pico" # the default
+ui.editor = "pico" # the default on Unix
 # ui.editor = "vim"
 
 ui.diff-editor = "meld" # default, requires meld to be installed

docs/tutorial.md

···
 instead of "Hello". Let's start by describing the change (adding a
 commit message) so we don't forget what we're working on:
 ```shell script
-# This will bring up $EDITOR (or `pico` by default). Enter something like
-# "Say goodbye" in the editor and then save the file and close the editor.
+# This will bring up $EDITOR (or `pico` or `Notepad` by default). Enter
+# something like "Say goodbye" in the editor and then save the file and close
+# the editor.
 $ jj describe
 Working copy now at: e427edcfd0ba Say goodbye
 ```