Adds nimrod to backend examples.

doc/backends.txt

@@ -141,9 +141,75 @@ To wrap native code, take a look at the `c2nim tool <c2nim.html>`_ which helps
 with the process of scanning and transforming header files into a Nimrod
 interface.
 
-Example in C.
+C invocation example
+~~~~~~~~~~~~~~~~~~~~
 
-Example in JS.
+Create a ``logic.c`` file with the following content:
+
+.. code-block:: c
+  int addTwoIntegers(int a, int b)
+  {
+    return a + b;
+  }
+
+Create a ``calculator.nim`` file with the following content:
+
+.. code-block:: nimrod
+
+  {.compile: "logic.c".}
+  proc addTwoIntegers(a, b: int): int {.importc.}
+
+  when isMainModule:
+    echo addTwoIntegers(3, 7)
+
+With these two files in place, you can run ``nimrod c -r calculator.nim`` and
+the Nimrod compiler will compile the ``logic.c`` file in addition to
+``calculator.nim`` and link both into an executable, which outputs ``10`` when
+run. Another way to link the C file statically and get the same effect would
+be remove the line with the ``compile`` pragma and run the following typical
+Unix commands::
+
+    $ gcc -c logic.c
+    $ ar rvs mylib.a logic.o
+    $ nimrod c --passL:mylib.a -r calculator.nim
+
+Just like in this example we pass the path to the ``mylib.a`` library (and we
+could as well pass ``logic.o``) we could be passing switches to link any other
+static C library.
+
+
+JavaScript invocation example
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Create a ``host.html`` file with the following content:
+
+.. code-block::
+
+  <html><body>
+  <script type="text/javascript">
+  function addTwoIntegers(a, b)
+  {
+    return a + b;
+  }
+  </script>
+  <script type="text/javascript" src="calculator.js"></script>
+  </body></html>
+
+Create a ``calculator.nim`` file with the following content (or reuse the one
+from the previous section):
+
+.. code-block:: nimrod
+
+  proc addTwoIntegers(a, b: int): int {.importc.}
+
+  when isMainModule:
+    echo addTwoIntegers(3, 7)
+
+Compile the Nimrod code to JavaScript with ``nimrod js -o:calculator.js
+calculator.nim`` and open ``host.html`` in a browser. If the browser supports
+javascript, you should see the value ``10``. In JavaScript the `echo proc
+<system.html#echo>`_ will modify the HTML DOM and append the string. Use the
+`dom module <dom.html>`_ for specific DOM querying and modification procs.
 
 
 Backend code calling Nimrod