docs/wamr: initial WAMR guide

This briefs how to get started with WAMR in NuttX.

Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>

Documentation/applications/interpreters/wamr/index.rst

@@ -1,3 +1,53 @@
 ==================================
 ``wamr`` Webassembly Micro Runtime
 ==================================
+
+This guides explains how to try WAMR on NuttX.
+
+Install WASI SDK
+================
+
+We need to be able to build WASM programs. This can be done by installing the ``wasi-sdk`` as shown in the `WAMR guide <https://wamr.gitbook.io/document/basics/getting-started/host_prerequsites>`_.
+
+Make sure the installation is reachable via ``/opt/wasi-sdk`` on your host, as this is expected by the build script of the WASM hello world sample below.
+
+Building NuttX
+==============
+
+We use the `sim/wamr` config to build WAMR with NuttX. Note that at this writing, the that CMake scripts don't work for this configuration. For now, please use the makefile build instead:
+
+.. code:: console
+
+   $ cd nuttx
+   $ tools/configure.sh sim/wamr
+   $ make -j4
+   $ ls -l nuttx
+   -rwxrwxr-x 1 yf yf 4176376 Jun 10 08:11 nuttx
+
+This will generate a ``nutxx`` binary. Also a WASM sample is available in the folder ``apps/interpreters/wamr/wamr/product-mini/app-samples/hello-world`` folder. We build the sample as follows:
+
+.. code:: console
+
+   $ cd apps/interpreters/wamr/wamr/product-mini/app-samples/hello-world
+   $ ./build.sh
+   $ ls -l test.wasm
+   -rwxrwxr-x 1 yf yf  413 Jun 10 08:18 test.wasm
+
+The ``test.wasm`` program should be accessible from NuttX later.
+
+Try WAMR in NSH
+===============
+
+Copy the ``test.wasm`` to the folder where the ``nuttx`` program lives, then run ``./nuttx`` to kick off NuttX and run ``iwasm /data/test.wasm`` from NSH:
+
+.. code:: console
+
+   $ ./nuttx
+
+   NuttShell (NSH) NuttX-12.4.0
+   nsh> iwasm /data/test.wasm
+   Hello world!
+   buf ptr: 0x1460
+   buf: 1234
+   nsh>
+