[Rev 01] RFR: 6684: Adding CONTRIBUTING.md file

[Marcus Hirt]

> 6684: Adding CONTRIBUTING.md file

The pull request has been updated with 1 additional commit.

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Added commits:
 - 8bfee00f: Adding information on commit message format

Changes:
  - all: https://git.openjdk.java.net/jmc/pull/46/files
  - new: https://git.openjdk.java.net/jmc/pull/46/files/47da1634..8bfee00f

Webrevs:
 - full: https://webrevs.openjdk.java.net/jmc/46/webrev.01
 - incr: https://webrevs.openjdk.java.net/jmc/46/webrev.00-01

  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jmc/pull/46.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/46/head:pull/46

PR: https://git.openjdk.java.net/jmc/pull/46