Update README.md

Add basic usage information

README.md

@@ -1,2 +1,64 @@
 # set-property-maven-plugin
-Set project variables dynamically while building a maven project
+**Set project properties dynamically while building a maven project**
+
+This plugin intends to help out other plugins by defining project properties via build-time.
+Add the following to your pom to use the plugin:
+
+```
+<pluginRepositories>
+  <repository>
+    <id>matzes-repo</id>
+    <url>http://matzefratze123.de/artifactory/release</url>
+  </repository>
+</pluginRepositories>
+```
+
+The plugin only provides one goal: set-properties
+This goal evaluates a condition and decides based on the configuration which properties need to be set.
+
+Example configuration:
+
+```
+<plugin>
+  <groupId>de.matzefratze123</groupId>
+  <artifactId>set-property-maven-plugin</artifactId>
+  <version>1.0.1</version>
+    <executions>
+      <execution>
+        <id>execution-id</id>
+        <!-- Default phase is 'validate' if not specified -->
+        <phase>validate</phase>
+        <goals>
+          <goal>set-properties</goal>
+        </goals>
+        <configuration>
+          <operations>
+            <operation>
+              <!-- This is the condition for which it compares the string with another string -->
+              <!-- In this example it compares the pom's version and checks wether it's a snapshot or not -->
+              <condition>
+                <string>${project.version}</string>
+                <operator>EQUALS_REGEX</operator>
+                <operand>.*-SNAPSHOT</operand>
+              </condition>
+              <!-- Define properties to be set when the condition above is true -->
+              <setpropertiestrue>
+                <setproperty>
+                  <property>deploy.url</property>
+                  <value>http://example.com/snapshots</value>
+                </setproperty>
+              </setpropertiestrue>
+              <!-- Define properties to be set when the condition above is false -->
+              <setpropertiesfalse>
+                <setproperty>
+                  <property>deploy.url</property>
+                  <value>http://example.com/releases</value>
+                </setproperty>
+              </setpropertiesfalse>
+            </operation>
+          </operations>
+        </configuration>
+      </execution>
+    </executions>    
+  </plugin>
+  ```