Make CONTRIBUTING.md all caps as per the Charter

According to the official Charter at
https://www.openbmc.org/wp-content/uploads/sites/62/2018/03/charter_openbmc_02142018.pdf
the file must be named literally `CONTRIBUTING`.
That is, all caps.

This has been discussed in review comments for
https://gerrit.openbmc-project.xyz/9948

Change-Id: I91697e89f9fcb812ad8928a62c4b6550e9e36291
Signed-off-by: Alexander Amelkin <a.amelkin@yadro.com>
diff --git a/contributing.md b/CONTRIBUTING.md
similarity index 100%
rename from contributing.md
rename to CONTRIBUTING.md
diff --git a/README.md b/README.md
index 557ac36..77d47f1 100644
--- a/README.md
+++ b/README.md
@@ -27,7 +27,7 @@
  - [cheatsheet.md](cheatsheet.md): Quick reference for some common
    development tasks
 
- - [contributing.md](contributing.md): Guidelines for contributing to
+ - [CONTRIBUTING.md](CONTRIBUTING.md): Guidelines for contributing to
    OpenBMC
 
  - [kernel-development.md](kernel-development.md): Reference for common