README.TXT: add README to describe how to this repository

add description about which patches we should inclued here,
and how to apply patches here.
also rename LOLLIPOP-EXPERIMENTAL-PATCHSET to LOLLIPOP-STABLE-PATCHSET,
and make a link LOLLIPOP-EXPERIMENTAL-PATCHSET to LOLLIPOP-STABLE-PATCHSET
so that the builds will work without any change

Change-Id: Icc57be595a5bdbc2df6e48f7a7d801952e732f8b
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>
2 files changed