Augment documentation with use of Bazel

.gitignore

@@ -3,6 +3,7 @@
 *.so
 .*.swp
 coverage.out
+/astgen/stdast.go
 /bazel-bin
 /bazel-genfiles
 /bazel-go-jsonnet

README.md

@@ -9,14 +9,11 @@
 [Coverage Status Widget]: https://coveralls.io/repos/github/google/go-jsonnet/badge.svg?branch=master
 [Coverage Status]: https://coveralls.io/github/google/go-jsonnet?branch=master
 
-This an implementation of [Jsonnet](http://jsonnet.org/) in pure Go.  It is
+This an implementation of [Jsonnet](http://jsonnet.org/) in pure Go. It is feature complete but is not as heavily exercised as the [Jsonnet C++ implementation](https://github.com/google/jsonnet).  Please try it out and give feedback.
-feature complete but is not as heavily exercised as the [Jsonnet C++
-implementation](https://github.com/google/jsonnet).  Please try it out and give
-feedback.
 
 This code is known to work on Go 1.8 and above. We recommend always using the newest stable release of Go.
 
-## Install instructions
+## Installation instructions
 
 ```
 go get github.com/google/go-jsonnet/cmd/jsonnet
@@ -27,8 +24,31 @@ go get github.com/google/go-jsonnet/cmd/jsonnet
 ```bash
 git clone github.com/google/go-jsonnet
 cd go-jsonnet
+git submodule init
+git submodule update
+go run cmd/dumpstdlibast/dumpstdlibast.go > astgen/stdast.go
 go build ./cmd/jsonnet
 ```
+To build with [Bazel](https://bazel.build/) instead:
+```bash
+git clone github.com/google/go-jsonnet
+cd go-jsonnet
+git submodule init
+git submodule update
+bazel build //cmd/jsonnet
+```
+The resulting _jsonnet_ program will then be available at a platform-specific path, such as _bazel-bin/cmd/jsonnet/darwin_amd64_stripped/jsonnet_ for macOS.
+
+Bazel also accommodates cross-compiling the program. To build the _jsonnet_ program for various popular platforms, run the following commands:
+
+Target platform | Build command
+--------------- | -------------------------------------------------------------------------------------
+Current host    | _bazel build //cmd/jsonnet_
+Linux           | _bazel build --platforms=@io_bazel_rules_go//go/toolchain:linux_amd64 //cmd/jsonnet_
+macOS           | _bazel build --platforms=@io_bazel_rules_go//go/toolchain:darwin_amd64 //cmd/jsonnet_
+Windows         | _bazel build --platforms=@io_bazel_rules_go//go/toolchain:windows_amd64 //cmd/jsonnet_
+
+For additional target platform names, see the per-Go release definitions [here](https://github.com/bazelbuild/rules_go/blob/master/go/private/sdk_list.bzl#L21-L31) in the _rules_go_ Bazel package.
 
 ## Build instructions (go 1.8 - 1.10)
 
@@ -36,6 +56,9 @@ go build ./cmd/jsonnet
 go get -u github.com/google/go-jsonnet
 cd $GOPATH/src/github.com/google/go-jsonnet
 go get -u .
+git submodule init
+git submodule update
+go run cmd/dumpstdlibast/dumpstdlibast.go > astgen/stdast.go
 go build ./cmd/jsonnet
 ```
 
@@ -47,9 +70,7 @@ go build ./cmd/jsonnet
 
 ## Implementation Notes
 
-We are generating some helper classes on types by using
+We are generating some helper classes on types by using http://clipperhouse.github.io/gen/.  Do the following to regenerate these if necessary:
-http://clipperhouse.github.io/gen/.  Do the following to regenerate these if
-necessary:
 
 ```bash
 go get github.com/clipperhouse/gen
@@ -60,15 +81,26 @@ go generate
 
 ## Updating and modifying the standard library
 
-Standard library source code is kept in `cpp-jsonnet` submodule,
+Standard library source code is kept in `cpp-jsonnet` submodule, because it is shared with [Jsonnet C++
-because it is shared with [Jsonnet C++
 implementation](https://github.com/google/jsonnet).
 
-For perfomance reasons we perform preprocessing on the standard library,
+For perfomance reasons we perform preprocessing on the standard library, so for the changes to be visible, regeneration is necessary:
-so for the changes to be visible, regeneration is necessary:
 
 ```bash
-./reset_stdast_go.sh && go run cmd/dumpstdlibast/dumpstdlibast.go
+go run cmd/dumpstdlibast/dumpstdlibast.go > astgen/stdast.go
 ```
 
-The above command recreates `ast/stdast.go` which puts the desugared standard library into the right data structures, which lets us avoid the parsing overhead during execution.
+The above command creates the _astgen/stdast.go_ file which puts the desugared standard library into the right data structures, which lets us avoid the parsing overhead during execution. Note that this step is not necessary to perform manually when building with Bazel; the Bazel target regenerates the _astgen/stdast.go_ (writing it into Bazel's build sandbox directory tree) file when necessary.
+
+## Keeping the Bazel files up to date
+Note that we maintain the Go-related Bazel targets with [the Gazelle tool](https://github.com/bazelbuild/bazel-gazelle). The Go module (_go.mod_ in the root directory) remains the primary source of truth. Gazelle analyzes both that file and the rest of the Go files in the repository to create and adjust appropriate Bazel targets for building Go packages and executable programs.
+
+After changing any dependencies within the files covered by this Go module, it is helpful to run _go mod tidy_ to ensure that the module declarations match the state of the Go source code. In order to synchronize the Bazel rules with material changes to the Go module, run the following command to invoke [Gazelle's `update-repos` command](https://github.com/bazelbuild/bazel-gazelle#update-repos):
+```bash
+bazel run //:gazelle -- update-repos -from_file=go.mod
+```
+
+Similarly, after adding or removing Go source files, it may be necessary to synchronize the Bazel rules by running the following command:
+```bash
+bazel run //:gazelle
+```