Move Bazel docs into versioned directory.

* Move all Bazel docs (excluding main page, search page, and blog)
  into versions/master directory.
* Replace all original pages with redirects.
* Add Jekyll config with default_version setting to specify the default
  version to redirect docs to.
* Add Jekyll config with version_prefix setting specific to pages under
  each version directory.
* Update layouts to generate links to pages for the same version with the
  version_prefix.
* Update Blaze release script to copy docs from
  third_party/bazel/site/versions/master

Changes to follow this CL:

* Separate navigation from layouts so that navigation can be versioned
  as well.
* Add tool for cutting a release of Bazel docs and copies them into a new
  version directory.

Bug: #579

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MOS_MIGRATED_REVID=128510319

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diff --git a/site/versions/master/docs/getting-started.md b/site/versions/master/docs/getting-started.md
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+++ b/site/versions/master/docs/getting-started.md
@@ -0,0 +1,97 @@
+---
+layout: documentation
+title: Getting Started
+---
+
+# Getting Started with Bazel
+
+## Setup
+
+Use the [installation instructions](/docs/install.html) to install a copy of
+Bazel on your machine.
+
+## Using a Workspace
+
+All Bazel builds take place in a [_workspace_](/docs/build-ref.html#workspaces),
+a directory on your filesystem that contains source code for the software you
+want to build, as well symbolic links to directories that contain the build
+outputs (for example, `bazel-bin` and `bazel-out`). The location of the
+workspace directory is not significant, but it must contain a file called
+`WORKSPACE` in the top-level directory; an empty file is a valid workspace.
+The `WORKSPACE` file can be used to reference
+[external dependencies](/docs/external.html) required to build the outputs.
+One workspace can be shared among multiple projects if desired.
+
+```bash
+$ touch WORKSPACE
+```
+
+## Creating a Build File
+
+To know which targets can be built in your project, Bazel inspects `BUILD`
+files. They are written in Bazel's build language which is syntactically
+similar to Python. Usually they are just a sequence of declarations of rules.
+Each rule specifies its inputs, outputs, and a way to compute the outputs from
+the inputs.
+
+The rule probably most familiar to people who have used `Makefile`s before (as
+it is the only rule available there) is the
+[genrule](/docs/be/general.html#genrule), which specifies how the output can
+be generated by invoking a shell command.
+
+```
+genrule(
+  name = "hello",
+  outs = ["hello_world.txt"],
+  cmd = "echo Hello World > $@",
+)
+```
+
+The shell command may contain [Make variables](/docs/be/make-variables.html).
+
+Using the above `BUILD` file, you can ask Bazel to generate the target.
+
+```
+$ bazel build :hello
+.
+INFO: Found 1 target...
+Target //:hello up-to-date:
+  bazel-genfiles/hello_world.txt
+INFO: Elapsed time: 2.255s, Critical Path: 0.07s
+```
+
+We note two things. First, targets are normally referred to by their
+[label](/docs/build- ref.html#labels), which is specified by the
+[name](/docs/be/general.html#genrule.name) attribute of the rule. (Referencing
+them by the output file name is also possible, but this is not the preferred
+way.) Second, Bazel puts the generated files into a separate directory (the
+`bazel-genfiles` directory is actually a symbolic link) so as not to pollute
+your source tree.
+
+Rules may use the output of other rules as input, as in the following
+example. Again, the generated sources are referred to by their label.
+
+```
+genrule(
+  name = "hello",
+  outs = ["hello_world.txt"],
+  cmd = "echo Hello World > $@",
+)
+
+genrule(
+  name = "double",
+  srcs = [":hello"],
+  outs = ["double_hello.txt"],
+  cmd = "cat $< $< > $@",
+)
+```
+
+Finally, note that, while the [genrule](/docs/be/general.html#genrule) might
+seem familiar, it usually is _not_ the best rule to use. It is preferrable to
+use one of the specialized [rules](/docs/be/overview.html#rules) for various
+languages.
+
+# Next Steps
+
+Next, check out the tutorial on building [java](/docs/tutorial/java.html)
+or [C++](/docs/tutorial/cpp.html) programs.