add caros-app-mix documentation

docs/caros-app-mix.md

@@ -0,0 +1,71 @@
+# caros-app-mix
+
+The caros-app-mix class is designed to build a caros app using mix.
+
+## Usage
+
+The `unimux` recipe serves as an example for the usage of the `caros-app-mix` class:
+
+```
+DESCRIPTION = "Universal API Multiplexer"
+SECTION = "net"
+LICENSE = "MPL-2.0"
+LIC_FILES_CHKSUM = "file://LICENSE;md5=815ca599c9df247a0c7f619bab123dad"
+
+PR = "r1"
+
+inherit caros-app-mix caros-service
+include urilock_${PN}_${PV}.inc
+
+CAROS_APP_SERVICE_${PN} = "unimux.service"
+
+APP_PREFIX = "/usr/caros-apps"
+SYSCONFIG_PREFIX = "${sysconfdir}"
+
+SRC_URI += "git://github.com/carosio/unimux.git;protocol=git"
+
+SRCREV = "b70705df963a94539ad34abe52f58359c0767c9c"
+
+S = "${WORKDIR}/git"
+```
+
+As seen in the `unimux` recipe a few parameters need to be set.
+First of all caros-app-mix needs to be included. In the case of `unimux` the
+installation directory is changed to `/usr/caros-apps`. And the configuration
+directory to `/etc` witch is the default value of the `sysconfdir` variable set
+by bitbake.
+
+## Variables
+
+These are the variables and there default values used by the `caros-app-mix`
+class to specify installation and configuration for the applications build.
+
+| Variables                | Usage                                           | Default Value                         |
+|:-------------------------|:------------------------------------------------|:--------------------------------------|
+| `APPNAME`                | name of the application                         | `${PN}`                               |
+| `APPVERSION`             | version of the application                      | `${PV}`                               |
+| `REL_NAME`               | name of elixir application                      | `${APPNAME}`                          |
+| `REL_VSN`                | version of elixir application                   | `${APPVERSION`                        |
+| `APP_PREFIX`             | installation directory                          | `/opt/apps`                           |
+| `SYSCONFIG_PREFIX`       | configuration directory                         | `${sysconfdir}/apps`                  |
+| `CONFFILE`               | configuration file path for appctl              | `${SYSCONFIG_PREFIX}/${APPNAME}.conf` |
+
+
+## Generating the urilock
+
+The urilock holds all dependencies from the `mix.lock` file located in the
+source repository of an elixir application.
+
+To generate the `urilock` simply execute:
+
+```
+./gen.py unimux/mix.lock > urilock_unimux_1.2.10.inc
+```
+
+The generated `urilock`-file needs to be placed next to the recipe. Also it needs to be specialy named:
+
+```
+urilock_<packagename>_<packageversion>.inc
+```
+
+This naming scheem is used to match the `include` line in the recipes, see example recipe above.