Adding to contribution.md.

CONTRIBUTING.md

+# Topic-based branch development
+A topic branch is a short-lived branch that you create for a single focus of work.
+Generally, short-lived is less than 6 months. The work can be bug fixes, feature development or design testing.
+It is good practice to always use a branch when introducing changes.
+This allows the master to remain passing and all subsequent branches to start clean.
+
+## In pratice
+### Getting started
+After you have cloned the project
+```
+git clone git@code.ornl.gov:jap/radix radix
+Cloning into 'radix'...
+remote: Counting objects: 893, done.
+remote: Compressing objects: 100% (384/384), done.
+remote: Total 893 (delta 523), reused 852 (delta 484)
+Receiving objects: 100% (893/893), 247.71 KiB | 95.00 KiB/s, done.
+Resolving deltas: 100% (523/523), done.
+Checking connectivity... done.
+```
+Checkout and create a local branch
+```
+git checkout -b featurex
+Switched to a new branch 'contribution_guide'
+```
+You now have a local branch `contribution_guide`
+```
+git branch -l
+* contribution_guide
+  master
+```
+This branch is not in the originating repository.
+```
+git branch -r
+  origin/HEAD -> origin/master
+  origin/master
+```
+### Making the first push
+When you are ready to push your changes
+