docs: build: add named anchor tags for flags

With this, the sections are linked from the "options" table when
producing the documentation on docs.docker.com

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/reference/commandline/build.md

@@ -326,7 +326,7 @@ project contains multiple Dockerfiles that expect to ignore different sets of
 files.
 
 
-### Tag an image (-t)
+### <a name=tag></a> Tag an image (-t, --tag)
 
 ```console
 $ docker build -t vieux/apache:2.0 .
@@ -346,7 +346,7 @@ For example, to tag an image both as `whenry/fedora-jboss:latest` and
 $ docker build -t whenry/fedora-jboss:latest -t whenry/fedora-jboss:v2.1 .
 ```
 
-### Specify a Dockerfile (-f)
+### <a name=file></a> Specify a Dockerfile (-f, --file)
 
 ```console
 $ docker build -f Dockerfile.debug .
@@ -393,17 +393,17 @@ the command line.
 > repeatable builds on remote Docker hosts. This is also the reason why
 > `ADD ../file` does not work.
 
-### Use a custom parent cgroup (--cgroup-parent)
+### <a name=cgroup-parent></a> Use a custom parent cgroup (--cgroup-parent)
 
 When `docker build` is run with the `--cgroup-parent` option the containers
 used in the build will be run with the [corresponding `docker run` flag](../run.md#specify-custom-cgroups).
 
-### Set ulimits in container (--ulimit)
+### <a name=ulimit></a> Set ulimits in container (--ulimit)
 
 Using the `--ulimit` option with `docker build` will cause each build step's
 container to be started using those [`--ulimit` flag values](run.md#set-ulimits-in-container---ulimit).
 
-### Set build-time variables (--build-arg)
+### <a name=build-arg></a> Set build-time variables (--build-arg)
 
 You can use `ENV` instructions in a Dockerfile to define variable
 values. These values persist in the built image. However, often
@@ -441,13 +441,13 @@ $ docker build --build-arg HTTP_PROXY .
 This is similar to how `docker run -e` works. Refer to the [`docker run` documentation](https://docs.docker.com/engine/reference/commandline/run/#set-environment-variables--e---env---env-file)
 for more information.
 
-### Optional security options (--security-opt)
+### <a name=security-opt></a> Optional security options (--security-opt)
 
 This flag is only supported on a daemon running on Windows, and only supports
 the `credentialspec` option. The `credentialspec` must be in the format
 `file://spec.txt` or `registry://keyname`.
 
-### Specify isolation technology for container (--isolation)
+### <a name=isolation></a> Specify isolation technology for container (--isolation)
 
 This option is useful in situations where you are running Docker containers on
 Windows. The `--isolation=<value>` option sets a container's isolation
@@ -463,7 +463,7 @@ Linux namespaces. On Microsoft Windows, you can specify these values:
 
 Specifying the `--isolation` flag without a value is the same as setting `--isolation="default"`.
 
-### Add entries to container hosts file (--add-host)
+### <a name=add-host></a> Add entries to container hosts file (--add-host)
 
 You can add other hosts into a container's `/etc/hosts` file by using one or
 more `--add-host` flags. This example adds a static address for a host named
@@ -471,7 +471,7 @@ more `--add-host` flags. This example adds a static address for a host named
 
     $ docker build --add-host=docker:10.180.0.1 .
 
-### Specifying target build stage (--target)
+### <a name=target></a> Specifying target build stage (--target)
 
 When building a Dockerfile with multiple build stages, `--target` can be used to
 specify an intermediate build stage by name as a final stage for the resulting
@@ -489,7 +489,7 @@ FROM alpine AS production-env
 $ docker build -t mybuildimage --target build-env .
 ```
 
-### Custom build outputs
+### <a name=output></a> Custom build outputs (--output)
 
 By default, a local container image is created from the build result. The
 `--output` (or `-o`) flag allows you to override this behavior, and a specify a
@@ -582,7 +582,7 @@ vndr
 > [enable BuildKit](../builder.md#buildkit) or use the [buildx](https://github.com/docker/buildx)
 > plugin which provides more output type options.
 
-### Specifying external cache sources
+### <a name=cache-from></a> Specifying external cache sources (--cache-from)
 
 In addition to local build cache, the builder can reuse the cache generated from
 previous builds with the `--cache-from` flag pointing to an image in the registry.
@@ -625,7 +625,7 @@ $ docker build --cache-from myname/myapp .
 > plugin. The previous builder has limited support for reusing cache from
 > pre-pulled images.
 
-### Squash an image's layers (--squash) (experimental)
+### <a name=squash></a> Squash an image's layers (--squash) (experimental)
 
 #### Overview