docs: create initial documentation subdirectory structure

As the number of meta-realtime users grows, the need to document various
parts of the layer grows as well. Rather than rely only on wiki and online
docs, we'll create a layer-local holding tank for relevant bits of
documentation.

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
meta-realtime: add rt-app, schedtool, define core-image-rt-extended, and append recipies-kernel

With this commit, all of the utilities and extensions required to test
sched_dealine with meta-realtime are in place.

*applications tested

1. rt-app
- "rt-app" is a test application that starts multiple periodic threads
  in order to simulate a real-time periodic load

  - run example

  root@qemux86:~# rt-app -t 100000:35000:d -D 1
  [rt-app] <notice> [0] Using SCHED_DEADLINE policy:
  [rt-app] <notice> [0] starting thread with period: 100000, exec:
  35000,deadline: 100000, priority: 10
  [rt-app] <notice> [0] Locking pages in memory
  idx	period	min_et	max_et	rel_st	start		end
  deadline	dur.	slack	Budget	Used Budget
  0	100000	35000	35000	64705	305724113	305759126
  305824105	35013	64979
  ...
  0	100000	35000	35000	965099	306624507	306659526
  306724105	35019	64578
  [rt-app] <notice> [0] Exiting.

  2. schedtool
  - scheduler test tool
  - run example
  root@qemux86:~# schedtool -E -t 10000:100000 -a 0 -e yes > /dev/null&
  root@qemux86:~# schedtool -E -t 30000:100000 -a 0 -e yes > /dev/null&
  root@qemux86:~# jobs
  [1]-  Running                 schedtool -E -t 10000:100000 -a 0 -e yes
  > /dev/null &
  [2]+  Running                 schedtool -E -t 30000:100000 -a 0 -e yes
  > /dev/null &

  $ top
  Mem: 33616K used, 84308K free, 0K shrd, 2684K buff, 13904K cached
  CPU:  37% usr   5% sys   0% nic  56% idle   0% io   0% irq   0% sirq
  Load average: 911.65 428.84 84.32 35501/62 715
  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
  714   688 root     R     2352   2%  28% yes
  713   688 root     R     2352   2%   9% yes
  715   688 root     R     2724   2%   4% top

Signed-off-by: Insop Song <insop.song@gmail.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Merge branch 'master' of git://git.yoctoproject.org/meta-realtime