[doc] Add contribution.md and .gitmessage template

fix #29 (closed)

@keu-computervision PTAL

CONTRIBUTION.md

@@ -2,7 +2,11 @@
 
 ## Commit convention
 
-Developers are encouraged to use the provided [gitmessage template](Documentation/.gitmessage), so every commit message follows the same convention.
+Developers are encouraged to use the provided [gitmessage template](Documentation/.gitmessage) in their [git configuration](https://git-scm.com/book/en/v2/Customizing-Git-Git-Configuration#_commit_template), so every commit message follows the same convention.
+
+```bash
+$ git config --global commit.template <LVCore_path>/Documentation/.gitmessage
+```
 
 Adopting a commit convention, has multiple advantages:
 * enforce coherence