init usage section

Author: bcicen

README.md

@@ -6,3 +6,19 @@ Small Python library for interacting with devpi servers via web API
 ```python
 pip install devpi-tools
 ```
+
+## Usage
+
+```python
+from devpi_tools import DevpiClient
+
+client = DevpiClient('http://127.0.0.1:3141')
+
+client.indexes # list all indexes
+index = client.index('/root/pypi') # or fetch a single index
+
+index.projects # list all projects
+project = index.project('devpi-tools') # or fetch a single project/package by name
+
+project.versions #list of uploaded versions
+```