doc: Add anchors to dhall sections

This will ensure the sections have stable links as well as prevent conflicts (pandoc uses heading text for ids and DocBook requires unique ids across the book).

doc/languages-frameworks/dhall.section.md

@@ -5,7 +5,7 @@ support for importing Dhall expressions, which is documented here:
 
 * [`dhall-lang.org` - Installing packages](https://docs.dhall-lang.org/tutorials/Language-Tour.html#installing-packages)
 
-## Remote imports
+## Remote imports {#ssec-dhall-remote-imports}
 
 Nixpkgs bypasses Dhall's support for remote imports using Dhall's
 semantic integrity checks.  Specifically, any Dhall import can be protected by
@@ -32,7 +32,7 @@ example, the Prelude Dhall package uses `pkgs.fetchFromGitHub` to fetch the
 to fetch Dhall code ensures that Dhall packages built using Nix remain pure and
 also behave well when built within a sandbox.
 
-## Packaging a Dhall expression from scratch
+## Packaging a Dhall expression from scratch {#ssec-dhall-packaging-expression}
 
 We can illustrate how Nixpkgs integrates Dhall by beginning from the following
 trivial Dhall expression with one dependency (the Prelude):
@@ -117,7 +117,7 @@ in
 $ nix build --file ./example.nix dhallPackages.true
 ```
 
-## Contents of a Dhall package
+## Contents of a Dhall package {#ssec-dhall-package-contents}
 
 The above package produces the following directory tree:
 
@@ -224,7 +224,7 @@ $ cat ./result/source.dhall
 …
 ```
 
-## Packaging functions
+## Packaging functions {#ssec-dhall-packaging-functions}
 
 We already saw an example of using `buildDhallPackage` to create a Dhall
 package from a single file, but most Dhall packages consist of more than one
@@ -297,7 +297,7 @@ terms of `buildDhallPackage` that accepts the following arguments:
 Additionally, `buildDhallGitHubPackage` accepts the same arguments as
 `fetchFromGitHub`, such as `sha256` or `fetchSubmodules`.
 
-## `dhall-to-nixpkgs`
+## `dhall-to-nixpkgs` {#ssec-dhall-dhall-to-nixpkgs}
 
 You can use the `dhall-to-nixpkgs` command-line utility to automate
 packaging Dhall code.  For example:
@@ -342,7 +342,7 @@ $ dhall-to-nixpkgs directory ~/proj/dhall-semver
     }
 ```
 
-## Overriding dependency versions
+## Overriding dependency versions {#ssec-dhall-overriding-dependency-versions}
 
 Suppose that we change our `true.dhall` example expression to depend on an older
 version of the Prelude (19.0.0):
@@ -415,7 +415,7 @@ like this:
   };
 ```
 
-## Overrides
+## Overrides {#ssec-dhall-overrides}
 
 You can override any of the arguments to `buildDhallGitHubPackage` or
 `buildDhallDirectoryPackage` using the `overridePackage` attribute of a package.