Add documentation

Author: jayvdb

README.md

@@ -1 +1,19 @@
-# coverage_env_plugin
+# coverage_env_plugin
+
+Set environment variables of the environment markers
+
+Enable by adding the following to coverage configuration file such as `setup.cfg`:
+
+```
+[coverage:coverage_env_plugin]
+markers = True
+
+[coverage:run]
+markers = True
+
+plugins =
+    coverage_env_plugin
+    coverage_config_reload_plugin
+```
+
+Depends on [`coverage_config_reload_plugin`](https://github.com/jayvdb/coverage_config_reload_plugin).