Makes headings in documentation consistent

Fixes #10673.

Signed-off-by: Rick Wieman <git@rickw.nl>

docs/sources/reference/builder.md

@@ -1,8 +1,8 @@
-page_title: Dockerfile Reference
+page_title: Dockerfile reference
 page_description: Dockerfiles use a simple DSL which allows you to automate the steps you would normally manually take to create an image.
 page_keywords: builder, docker, Dockerfile, automation, image creation
 
-# Dockerfile Reference
+# Dockerfile reference
 
 **Docker can build images automatically** by reading the instructions
 from a `Dockerfile`. A `Dockerfile` is a text document that contains all
@@ -105,7 +105,7 @@ be treated as an argument. This allows statements like:
 Here is the set of instructions you can use in a `Dockerfile` for building
 images.
 
-### Environment Replacement
+### Environment replacement
 
 > **Note**: prior to 1.3, `Dockerfile` environment variables were handled
 > similarly, in that they would be replaced as described below. However, there
@@ -288,7 +288,7 @@ guide](/articles/dockerfile_best-practices/#build-cache) for more information.
 The cache for `RUN` instructions can be invalidated by `ADD` instructions. See
 [below](#add) for details.
 
-### Known Issues (RUN)
+### Known issues (RUN)
 
 - [Issue 783](https://github.com/docker/docker/issues/783) is about file
   permissions problems that can occur when using the AUFS file system. You
@@ -973,7 +973,7 @@ For example you might add something like this:
 
 > **Warning**: The `ONBUILD` instruction may not trigger `FROM` or `MAINTAINER` instructions.
 
-## Dockerfile Examples
+## Dockerfile examples
 
     # Nginx
     #

docs/sources/reference/commandline/cli.md

@@ -24,7 +24,7 @@ the `docker` command, your system administrator can create a Unix group called
 For more information about installing Docker or `sudo` configuration, refer to
 the [installation](/installation) instructions for your operating system.
 
-## Environment Variables
+## Environment variables
 
 For easy reference, the following list of environment variables are supported
 by the `docker` command line:
@@ -48,7 +48,7 @@ These Go environment variables are case-insensitive. See the
 [Go specification](http://golang.org/pkg/net/http/) for details on these
 variables.
 
-## Configuration Files
+## Configuration files
 
 The Docker command line stores its configuration files in a directory called
 `.docker` within your `HOME` directory. Docker manages most of the files in
@@ -2210,7 +2210,7 @@ application change:
    `--rm` option means that when the container exits, the container's layer is
    removed.
 
-#### Restart Policies
+#### Restart policies
 
 Use Docker's `--restart` to specify a container's *restart policy*. A restart
 policy controls whether the Docker daemon restarts a container after exit.

docs/sources/reference/run.md

@@ -156,7 +156,7 @@ Images using the v2 or later image format have a content-addressable identifier
 called a digest. As long as the input used to generate the image is unchanged,
 the digest value is predictable and referenceable.
 
-## PID Settings (--pid)
+## PID settings (--pid)
     --pid=""  : Set the PID (Process) Namespace mode for the container,
            'host': use the host's PID namespace inside the container
 
@@ -177,7 +177,7 @@ within the container.
 This command would allow you to use `strace` inside the container on pid 1234 on
 the host.
 
-## IPC Settings (--ipc)
+## IPC settings (--ipc)
 
     --ipc=""  : Set the IPC mode for the container,
                  'container:<name|id>': reuses another container's IPC namespace