cli: describe how to set a config value with apostrophes

Apostrophes are not uncommon in e.g. `user.name`, so let's help the
user by providing examples.

cli/src/commands/config/set.rs

@@ -38,8 +38,13 @@ pub struct ConfigSetArgs {
     /// New value to set
     ///
     /// The value should be specified as a TOML expression. If string value
-    /// doesn't contain any TOML constructs (such as array notation), quotes can
-    /// be omitted.
+    /// doesn't contain any TOML constructs (such as apostrophes or array
+    /// notation), quotes can be omitted. Note that the value may also need
+    /// shell quoting. The exact syntax depends on your shell. For example,
+    /// to set `foo.bar` to the string "don't" in Bash, use 
+    /// `jj config set --user foo.bar '"don'\''t"'`. In Fish, use
+    /// `jj config set --user foo.bar '"don\'t"'`. Alternatively, use
+    /// `jj config edit` to edit the TOML file directly.
     #[arg(required = true, value_parser = parse_value_or_bare_string)]
     value: ConfigValue,
     #[command(flatten)]

cli/tests/cli-reference@.md.snap

@@ -642,7 +642,7 @@ Update config file to set the given option to a given value
 * `<NAME>`
 * `<VALUE>` — New value to set
 
-   The value should be specified as a TOML expression. If string value doesn't contain any TOML constructs (such as array notation), quotes can be omitted.
+   The value should be specified as a TOML expression. If string value doesn't contain any TOML constructs (such as apostrophes or array notation), quotes can be omitted. Note that the value may also need shell quoting. The exact syntax depends on your shell. For example, to set `foo.bar` to the string "don't" in Bash, use `jj config set --user foo.bar '"don'\''t"'`. In Fish, use `jj config set --user foo.bar '"don\'t"'`.  Alternatively, use `jj config edit` to edit the TOML file directly.
 
 ###### **Options:**