meta-openpower: enhance README.md

Add words to the layer README.  The existing README is somewhat terse.
Expand it some, adopting some of the conventions from other well-known
OE BSP layers (used meta-freescale as a template).

Briefly describe the goal of the layer.  The goals mention full
implementations for OpenPOWER reference platforms, which doesn't match
reality today; however, the current plan/thinking is to consolidate the
meta-foo layers for each reference platform into meta-openpower.

Added layer dependencies.  meta-openpower depends on oe-core,
meta-phosphor and meta-aspeed.

Add contributing guidelines and style guide.

(From meta-openpower rev: 259c9bad006ecdc814f5d9dbd0b718ca5559fb1e)

Change-Id: I737ac1960fe2e3ba38994e9a9c36c95de19f7746
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-openpower/README.md b/meta-openpower/README.md
index 5558eb1..df764b8 100644
--- a/meta-openpower/README.md
+++ b/meta-openpower/README.md
@@ -1,6 +1,48 @@
-OpenPOWER
-================
+OpenEmbedded/Yocto/OpenBMC BSP layer for OpenPOWER reference platforms
+======================================================================
 
-meta-openpower is the OpenPOWER layer and should be included in all OpenPOWER
-systems' bblayers.conf. More information on OpenPOWER can be found
+This layer provides support for the BMC firmware on OpenPOWER reference
+platforms, and/or a base upon which to create a BMC firmware implementation on
+any POWER system.
+
+```
+This layer depends on:
+
+URI: git://git.openembedded.org/openembedded-core
+layers: meta
+branch: master
+revision: HEAD
+
+URI: https://github.com/openbmc/meta-phosphor
+branch: master
+revision: HEAD
+
+URI: https://github.com/openbmc/meta-aspeed
+branch: master
+revision: HEAD
+```
+
+More information on OpenPOWER can be found
 [here](https://openpowerfoundation.org/).
+
+Contributing
+------------
+
+meta-openpower patches are reviewed using the Gerrit instance at
+https://gerrit.openbmc-project.xyz.
+
+Please submit patches to Gerrit.  More information on using Gerrit can be found
+[here](https://github.com/openbmc/docs/blob/master/CONTRIBUTING.md#submitting-changes-via-gerrit-server).
+https://github.com/openbmc/meta-openpower is a hosting mirror only and GitHub
+pull requests are not monitored and will not be accepted.
+
+Patch checklist.  Please ensure patches adhere to the following guidelines:
+
+ - meta-openpower uses the [OE style
+   guidelines](https://www.openembedded.org/wiki/Styleguide).
+ - follow [the seven rules of a great git commit
+   message](https://chris.beams.io/posts/git-commit/#seven-rules)
+
+For questions or help please come join us on the [mailing
+list](https://lists.ozlabs.org/listinfo/openbmc) or in
+[IRC](irc://freenode.net/openbmc).