Extend README, add basic user guide (#73)

Signed-off-by: Sebastian Kürten <[email protected]>

README.md

@@ -3,6 +3,78 @@
 Proj4J is a Java library for converting coordinates between different geospatial coordinate reference systems.
 It is designed to be compatible with `proj.4` parameters and derives some of its implementation from the `proj.4` sources.
 
+Proj4J is a project in the [LocationTech](http://www.locationtech.org) working group of the Eclipse Foundation.
+
+![LocationTech](locationtech_mark.png) 
+
+## User Guide
+
+Proj4J artifacts are available on maven central.
+
+### Using Proj4J with Maven
+
+To include Proj4J in a Maven project, add a dependency block like the following:
+
+```xml
+<properties>
+    <proj4j.version>1.1.3</proj4j.version>
+</properties>
+<dependency>
+    <groupId>org.locationtech.proj4j</groupId>
+    <artifactId>proj4j</artifactId>
+    <version>${proj4j.version}</version>
+</dependency>
+```
+
+### Using Proj4J with Gradle
+
+To include Proj4J in a Gradle project, add a dependency block like the following:
+
+```
+dependencies {
+    implementation 'org.locationtech.proj4j:proj4j:1.1.3'
+}
+```
+
+### Basic Usage
+
+The following examples give a quick intro on how to use Proj4J in common
+use cases.
+
+#### Transforming coordinates from WGS84 to UTM
+
+##### Obtaining CRSs by name
+
+```Java
+CRSFactory crsFactory = new CRSFactory();
+CoordinateReferenceSystem WGS84 = crsFactory.createFromName("epsg:4326");
+CoordinateReferenceSystem UTM = crsFactory.createFromName("epsg:25833");
+```
+
+##### Obtaining CRSs using parameters
+
+```Java
+CRSFactory crsFactory = new CRSFactory();
+CoordinateReferenceSystem WGS84 = crsFactory.createFromParameters("WGS84",
+    "+proj=longlat +datum=WGS84 +no_defs");
+CoordinateReferenceSystem UTM = crsFactory.createFromParameters("UTM",
+    "+proj=utm +zone=33 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs");
+```
+
+##### Transforming coordinates
+
+```Java
+CoordinateTransformFactory ctFactory = new CoordinateTransformFactory();
+CoordinateTransform wgsToUtm = ctFactory.createTransform(WGS84, UTM);
+// `result` is an output parameter to `transform()`
+ProjCoordinate result = new ProjCoordinate();
+wgsToUtm.transform(new ProjCoordinate(lon, lat), result);
+```
+
 ## Building, Testing and installing locally
 
 `mvn clean install`
+
+## Contributing
+
+If you are interested in contributing to Proj4J please read the [**Contributing Guide**](CONTRIBUTING.md).