Add README.md

Readme with GitHub flavored markdown containing the following
informations:

- How to build and install with cmake.
- Minimalistic example mappings for File and Directory.

Change-Id: Ib107cd623bb7ec598138d1d18bfd36b5de817aac
Signed-off-by: Mattijs Korpershoek <[email protected]>

Author: Mattijs Korpershoek

README.md

@@ -0,0 +1,85 @@
+# Filesystem plugin for the parameter-framework
+
+This is a file system plugin for the
+[parameter-framework](https://github.com/01org/parameter-framework)
+handling file system operations such as `read()` and `write()`.
+
+
+## Compiling
+
+You need to install the parameter-framework libraries
+and headers first (see the parameter-framework's
+[README](https://github.com/01org/parameter-framework/blob/master/README.md)).
+
+Generate the Makefiles with `cmake .` and build with `make`.
+If you installed the parameter-framework in a custom directory, you should add a
+`-DCMAKE_PREFIX_PATH=/path/to/custom/install` argument to `cmake` e.g:
+`cmake -DCMAKE_PREFIX_PATH=/home/myself/dev/pfw .` .
+
+If you want to install the plugin to a custom directory, you can add a
+`-DCMAKE_INSTALL_PREFIX=/path/to/install/dir` argument to `cmake` e.g:
+`cmake -DCMAKE_INSTALL_PREFIX=/home/myself/dev/pfw .` .
+
+Finally, install the libraries with `make install` .
+
+
+## Usage example
+
+In this example, we are going to control two leds (*ledA* and *ledB*) via sysfs
+on a raspberry pi. Let's imagine that the leds are connected on the *pin4* and
+*pin7* on the raspberry's GPIO.
+
+To enable sysfs for the pins, we must "export the pins" first:
+
+    echo "4" > /sys/class/gpio/export
+    echo "7" > /sys/class/gpio/export
+
+### Configuration file
+
+Here is the complete `rpifs-subsystem.xml` file:
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<Subsystem Name="RaspberryFS" Type="FS" Endianness="Little">
+    <ComponentLibrary>
+        <ComponentType Name="GpioPin">
+            <StringParameter Name="direction" Mapping="File:direction" MaxLength="3"
+             Description="the direction of the pin: can be out or in" />
+            <StringParameter Name="state" Mapping="File:value" MaxLength="1"
+             Description="the state of the pin: can be 0 or 1" />
+        </ComponentType>
+    </ComponentLibrary>
+    <InstanceDefinition>
+        <Component Name="ledA" Type="GpioPin" Mapping="Directory:/sys/class/gpio/gpio4"/>
+        <Component Name="ledB" Type="GpioPin" Mapping="Directory:/sys/class/gpio/gpio7"/>
+    </InstanceDefinition>
+</Subsystem>
+```
+
+When declaring an `InstanceDefinition` the `Directory` mapping must be given to
+the component. Here it points towards the directory containing the GPIO pin4
+sysfs directory.
+
+When describing a `ComponentType`, the `File:...` mapping must be given to each
+parameter. Here we have two parameters. Since we are describing a pin, we must
+provide the direction and the state.
+
+### Usage
+If we consider that the `pfw` command is a shorthand for `remote-process
+localhost 5001`(where 5001 is the port defined at the top-level
+parameter-framework configuration file), which can be used to interact with the
+parameter-framework.
+
+#### To initialize the leds:
+
+    pfw setTuningMode on
+    pfw setParameter /Raspberry/RaspberryFS/ledA/direction out
+    pfw setParameter /Raspberry/RaspberryFS/ledB/direction out
+
+#### To turn the led A on:
+
+    pfw setParameter /Raspberry/RaspberryFS/ledA/value 1
+
+#### To turn the led A off:
+
+    pfw setParameter /Raspberry/RaspberryFS/ledA/value 0
+