Fix typos and markdown layout in README.md

The "Development guidelines" section on the project github homepage
has several small problems:
- there are two steps numbered "3": changing the last one to "4"
- the "hotfix-" branch name appears in italic because the two dashes
  are interpreted as markdown: fix by using backquotes for branch names
- section 3 has a single bullet point: fix by adding "You may name ..."
  as the second bullet point
- step 4 doesn't appear on a new line unless there is a blank line just
  above: adding such a blank line above step 4, and also between each
  step of the section for extra consistency. Adding a blank line just
  above step 4 would work as well

README.md

@@ -16,15 +16,19 @@ The VIP logo was designed by Max Langer under the [CC BY-NC-SA license](https://
 git config --global user.name "Jeanne Tartempion"                  # not "tartempion" or "jtartempion" or "root"
 git config --global user.email "[email protected]"   # not "root@localhost"
 ```
+
 1. Developments are made in forks from the base repository. Developments lead to pull-requests that are merged by the owner(s) of the base repository.
-2. Starting from release 1.15, we adopt the branching model described [here](http://nvie.com/posts/a-successful-git-branching-model). 
-3. When working on a new feature: 
+
+2. Starting from release 1.15, we adopt the branching model described [here](http://nvie.com/posts/a-successful-git-branching-model).
+
+3. When working on a new feature:
 * In your fork, create a new feature branch from the development branch:
 ```
 git checkout -b new_feature develop
 ```
-You may name your branch anything except master, develop, release-*, or hotfix-*
-3. When feature development is finished:
+* You may name your branch anything except `master`, `develop`, `release-*`, or `hotfix-*`.
+
+4. When feature development is finished:
 * Push your commits to Github (your fork).
 * Make a pull request to merge feature branch (in your fork) to development branch (in the base repository).