docs: adjust heading names in guide

Signed-off-by: Gaoyang Zhang <gy@blurgy.xyz>

docs/config/guide/06-filename-manipulating.md

@@ -36,7 +36,7 @@ will have all its items populated to the exact path `/some/path/dot-target`,
 instead of `/some/path/.target`.
 :::
 
-## Per-group rules
+## Per-group Rules
 
 You might have guessed it: `rename` rules can also be specified on a per-group
 basis.  The way this works is that `dt-cli` processes renaming rules in the
@@ -71,7 +71,7 @@ capability it provides is defining [capturing groups].  Capturing groups can
 either be [named] or [numbered], which allows arbitrary manipulation to be
 applied to any synced items.
 
-### Repeating extension of an item
+### Example: <sub>Repeating the Extension of an Item</sub>
 
 To illustrate how capturing groups work, we try to have the destination items
 to repeat the extension name of their corresponding source items, via

docs/config/guide/07-templating.md

@@ -37,7 +37,7 @@ target = "~/.config"
 
 In this config example, we have two values under the `context.gui` section.
 
-## Writing templates
+## Writing Templates
 
 Templates are understood by `dt-cli` with the [Handlebars] syntax.  We can
 template the gtk settings file in the `gui` group (se above) as:
@@ -59,7 +59,7 @@ gtk-cursor-theme-size=24
 gtk-font-name=system-ui 15
 ```
 
-## Skipping rendering
+## Skipping Rendering
 
 By default, `dt-cli` treats all source files as templates to be rendered.
 Sometimes we want to skip rendering, for example when a source file is huge,