Add card script doc

Signed-off-by: Andreas Müller <schnitzeltony@gmail.com>

scripts/README-SDCard-write

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+This folder contains a collection of scripts to write images to (SD)cards. A
+simple GUI was implemented to make selections easy. This GUI is based on
+'dialog' [1] which should be part of common packages in most distros.
+
+
+There are three type of scripts:
+
+1. card-part: These type of scripts create partitions on the card as the
+   bootloaders expect them. This type of scripts are necessary only for
+   machines whose board support layer still builds images in 'old style' 
+   e.g rootfs as *.tar.bz2).
+2. card-write: These type of scripts write complete images (bootloader/
+   devicetrees/kernel/rootfs) onto card.
+   Machine defaults can be overriden by setting variables 
+   'Machine' / 'FindString' - see include/card-helpers.inc
+   function StartCardWrite.
+3. card-kernel-write: This family of scripts just overwrite kernel, devicetrees
+   and kernel modules on cards with image installed. These scripts are extremly
+   helpful for testing kernel/devicetree modififations or just updating kernel
+   on precious (=many settings applied / full of userdata) images.
+   Machine defaults can be overriden by setting variables 
+   'Machine' / 'KernelImageType' / 'FindString' - see include/card-helpers.inc
+   function StartCardKernelWrite.
+
+To reduce the GUI-dialogs displayed or avoid them completely all scripts can be
+called with the following parameters
+
+1. Card device path e.g '/dev/sdc'
+2. Source file to be written (either rootfs or kernel link with abiversion)
+3. su / sudo selection: Pass '1' for su or '2' for sudo
+
+
+Script structure:
+
+1. include/*helper.inc: These script snippets are included by other scripts and
+   contain useful functions to be re-used by other scripts.
+2. include/machine-*.inc: All machine specific definitions and function
+   overrides are found in these files.
+   The following variables should be set within them:
+   * DEFAULT_MACHINE_FAMILY: This variable is used to find machine specific
+     deploy-dir containing kernel/rootfs...
+     o Example contents are: '*imx*' / 'raspberrypi*'. 
+     o Defaults can be overriden by calling scripts with:
+       Machine=<override> <script>
+   * DEFAULT_FIND_ROOTFS: This string is passed to the call of 'find' and
+     reduces find result for file selection dialog on files containing rootfs
+     only.
+     o Example contents: '-name *.rpi-sdimg -type l' / 'raspberrypi*'.
+     o Defaults can be overriden by calling card-write scripts with:
+       FindString=<override> <script>
+   * DEFAULT_KERNEL_IMAGE_TYPE: This variable is mandatory to be set for
+     operating card-kernel script. The value depends on the kernel image format
+     machine's board support package prefers.
+     o Example contents: 'Image' / 'uImage' / 'zImage'.
+     o Defaults can be overriden by overwriting value after including
+       machine-*.inc - see ti-old-omap-card-kernel-write-overo.sh
+3. <soc>-card-<operation>[-board].sh: These are the scripts to be executed.
+   They typically just contain necessary includes and one call for desired
+   operation: StartCardWrite / StartCardKernelWrite. Sligly talored variants
+   are found in ti-old-omap-card-part.sh / ti-old-omap-card-kernel-write-overo.sh
+
+
+Howto create scripts for other socs/machines:
+
+1. Read above
+2. Create a machine/soc header include/machine-<your-machine>.inc containing
+   variables for defaults and function overrides.
+3. Create <soc>-card-<operation>[-board].sh scripts.

scripts/ti-old-omap-README

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-ti-old-omap:
-These scripts are used when using old image style (non WKS / dd) for TI 
-omap3/zitara machines. Intended for images build with meta-bbone and
-meta-gumstix-community (would like to let them die but we still have active
-products based on these very old layers).