doc: add "building node with ninja" guide

doc/guides/building-node-with-ninja.md

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+# Building Node with Ninja
+
+The purpose of this guide is to show how to build Node.js using [Ninja][], as doing so can be significantly quicker than using `make`. Please see [Ninja's site][Ninja] for installation instructions (unix only).
+
+To build Node with ninja, there are 4 steps that must be taken:
+
+1. Configure the project's OS-based build rules via `./configure` as usual.
+2. Use `tools/gyp_node.py -f ninja` to produce Ninja-buildable `gyp` output.
+3. Run `ninja -C out/Release` to produce a compiled release binary.
+4. Lastly, make symlink to `./node` using `ln -fs out/Release/node node`.
+
+When running `ninja -C out/Release` you will see output similar to the following if the build has succeeded:
+```
+ninja: Entering directory `out/Release`
+[4/4] LINK node, POSTBUILDS
+```
+
+The bottom line will change while building, showing the progress as `[finished/total]` build steps.
+This is useful output that `make` does not produce and is one of the benefits of using Ninja.
+Also, Ninja will likely compile much faster than even `make -j8` (or `-j<number of processor threads on your machine>`).
+
+## Considerations
+
+Ninja builds vary slightly from `make` builds. If you wish to run `make test` after, `make` will likely still need to rebuild some amount of Node.
+
+As such, if you wish to run the tests, it can be helpful to invoke the test runner directly, like so:
+`tools/test.py --mode=release message parallel sequential -J`
+
+## Alias
+
+`alias nnode='./configure && tools/gyp_node.py -f ninja && ninja -C out/Release && ln -fs out/Release/node node'`
+
+## Producing a debug build
+
+The above alias can be modified slightly to produce a debug build, rather than a release build as shown below:
+`alias nnodedebug='./configure && tools/gyp_node.py -f ninja && ninja -C out/Debug && ln -fs out/Debug/node node_g'`
+
+
+[Ninja]: https://martine.github.io/ninja/