improved readme

README.md

@@ -6,9 +6,32 @@ Automatically change `JAVA_HOME` based on current directory `pom.xml`
 
 For now, only Ubuntu and OSX are supported.
 
+### Usage
+
+```sh
+git clone https://github.com/caarlos0/jvm.git ~/.jvm
+
+# for bash
+echo "source ~/.jvm/jvm.sh" >> .bashrc
+
+# for zsh
+echo "source ~/.jvm/jvm.sh" >> .zshrc
+```
+
+Then, just `cd` to a java project folder. If the `pom.xml`  has a
+`<java.version>1.7</java.version>`, for example, jvm will try to
+set JDK7 to your PATH.
+
+If you don't have and don't want to have this in your project's pom,
+you can also do this:
+
+```sh
+echo 7 >> .java-version
+```
+
+
 ### TODO
 
 - Add support for more platforms (maybe via some config file);
 - Better documentation;
 - Tests;
-- Maybe use update-java-alternatives on ubuntu and /usr/libexec/java_home on mac