Update README (#19)

README.md

@@ -1,2 +1,44 @@
 # ros_introspect
-Pure Python library for working with the files in ROS packages
+
+ `ros_introspect` is a Pure Python library for working with the files in ROS packages in a structured way.
+It is compatible with both ROS 1 and ROS 2.
+
+You can specify the path directly.
+
+```
+from ros_introspect import Package
+package = Package('/full/path/geometry_msgs')
+```
+or you can use the built-in crawler to search recursively
+
+```
+from ros_introspect import find_packages
+
+for package in find_packages('/home/dlu/ros2_ws/src'):
+    print(package)
+```
+
+
+## The `Package` Class
+
+A `Package` is a path where the `$PATH/package.xml` exists and a collection of `PackageFile`s that are contained within that folder.
+
+Each of the package files are a subtype of `PackageFile` based on their functionality, with each of the subtypes being defined in `ros_introspect.components`, including...
+
+ * `package.xml`
+ * `CMakeLists.txt`
+ * Source code (Python or C++)
+ * ROS Interfaces, i.e. messages, services and actions
+ * DynamicReconfig configurations (ROS 1 only)
+ * Plugin XML, for use with `pluginlib`
+ * Launch files, both `XML` (ROS 1) and Python (ROS 2)
+ * Parameter files (`.yaml`)
+ * RViz configurations (`.rviz`)
+ * Robot model files (`.urdf` and `.xacro`)
+ * `setup.py` and `setup.cfg` for Python code
+ * Documentation (Markdown, RST, licenses, etc.)
+ * Miscellaneous Config files (various metadata like the `.github` folder)
+
+Everything that does not fall into one of those categories ends up as "Other"**
+
+**Excluding `.pyc`, `*~`, and `.git/` files