Fix basic Ruby syntax errors in docs example code

- Blocks should open with `do` and close with `end`.
- `...` is not valid Ruby syntax, so comment it out so that the user
  knows that it's a placeholder for "other things here".
- Reword the "header line details" in `Cask-Cookbook` otherwise RuboCop
  crashes even with an `end` because of the empty block. There was
  already an example of a valid header line in the first code block on
  the page, so it's not a big loss.

docs/Cask-Cookbook.md

@@ -29,13 +29,7 @@ Exception: `do` blocks such as `postflight` may enclose a block of pure Ruby cod
 
 ## Header line details
 
-The first non-comment line in a cask follows the form:
+The Cask name ([`<cask-token>`](#token-reference)) on the header line `cask <cask-token> do` should match the cask filename, without the `.rb` extension, enclosed in double quotes.
-
-```ruby
-cask "<cask-token>" do
-```
-
-[`<cask-token>`](#token-reference) should match the cask filename, without the `.rb` extension, enclosed in double quotes.
 
 There are currently some arbitrary limitations on cask tokens which are in the process of being removed. GitHub Actions will catch any errors during the transition.
 
@@ -1197,6 +1191,7 @@ cask "libreoffice" do
 
   url "https://download.documentfoundation.org/libreoffice/stable/#{version}/mac/#{folder}/LibreOffice_#{version}_MacOS_#{arch}.dmg",
       verified: "download.documentfoundation.org/libreoffice/stable/"
+end
 ```
 
 If the version number is different for each architecture, locate the unique `version` and (if checked) `sha256` stanzas within `on_arm` and `on_intel` blocks. Example (from [inkscape.rb](https://github.com/Homebrew/homebrew-cask/blob/11f6966bf17628b98895d64a61a4fb0bc1bb31bf/Casks/i/inkscape.rb#L1-L13)):
@@ -1215,6 +1210,7 @@ cask "inkscape" do
   end
 
   url "https://inkscape.org/gallery/item/#{version.csv.second}/Inkscape-#{version.csv.first}_#{arch}.dmg"
+end
 ```
 
 To adjust the installed version depending on the current macOS release, use a series of `on_<system>` blocks that cover the range of supported releases. Each block can contain stanzas that set which version to download and customize installation/uninstallation and livecheck behaviour for one or more releases. Example (from [calibre.rb](https://github.com/Homebrew/homebrew-cask/blob/482c34e950da8d649705f4aaea7b760dcb4b5402/Casks/c/calibre.rb#L1-L34)):
@@ -1244,6 +1240,7 @@ cask "calibre" do
       strategy :github_latest
     end
   end
+end
 ```
 
 Such `on_<system>` blocks can be nested and contain other stanzas not listed here. Examples: [calhash.rb](https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/c/calhash.rb), [openzfs.rb](https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/o/openzfs.rb), [r.rb](https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/r/r.rb), [wireshark.rb](https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/w/wireshark.rb)
@@ -1260,7 +1257,7 @@ In the exceptional case that the cask DSL is insufficient, it is possible to def
 cask "myapp" do
   module Utils
     def self.arbitrary_method
-      ...
+      # ...
     end
   end
 
@@ -1270,7 +1267,7 @@ cask "myapp" do
 
   url "https://#{Utils.arbitrary_method}"
   homepage "https://www.example.com/"
-  ...
+  # ...
 end
 ```
 

docs/Formula-Cookbook.md

@@ -546,7 +546,7 @@ end
 
 ```ruby
 stable do
-  # some other things...
+  # ...
 
   patch do
     url "https://example.com/example_patch.diff"
@@ -700,6 +700,7 @@ class Nginx < Formula
   url "https://nginx.org/download/nginx-1.23.2.tar.gz", using: :homebrew_curl
   sha256 "a80cc272d3d72aaee70aa8b517b4862a635c0256790434dbfc4d618a999b0b46"
   head "https://hg.nginx.org/nginx/", using: :hg
+end
 ```
 
 Homebrew offers these anonymous download strategies.
@@ -890,13 +891,14 @@ If you want to add an [`option`](https://rubydoc.brew.sh/Formula#option-class_me
 
 ```ruby
 class Yourformula < Formula
-  ...
+  # ...
   option "with-ham", "Description of the option"
   option "without-spam", "Another description"
 
   depends_on "foo" => :optional  # automatically adds a with-foo option
   depends_on "bar" => :recommended  # automatically adds a without-bar option
-  ...
+  # ...
+end
 ```
 
 And then to define the effects the [`option`](https://rubydoc.brew.sh/Formula#option-class_method)s have: