MINOR: Improve README

Mention Java 7 requirement, fix and improve formatting and remove obsolete reference to SVN website.

Author: Ismael Juma <ismael@juma.me.uk>

Reviewers: Sriharsha Chintalapani <harsha@hortonworks.com>, Jason Gustafson <jason@confluent.io>

Closes #677 from ijuma/mention-java-requirement-in-readme

README.md

@@ -2,18 +2,20 @@ Apache Kafka
 =================
 See our [web site](http://kafka.apache.org) for details on the project.
 
-You need to have [gradle](http://www.gradle.org/installation) installed.
+You need to have [Gradle](http://www.gradle.org/installation) and [Java](http://www.oracle.com/technetwork/java/javase/downloads/index.html) installed.
+
+Java 7 should be used for building in order to support both Java 7 and Java 8 at runtime.
 
 ### First bootstrap and download the wrapper ###
     cd kafka_source_dir
     gradle
 
-Now everything else will work
+Now everything else will work.
 
 ### Building a jar and running it ###
     ./gradlew jar  
 
-Follow instuctions in http://kafka.apache.org/documentation.html#quickstart
+Follow instructions in http://kafka.apache.org/documentation.html#quickstart
 
 ### Building source jar ###
     ./gradlew srcJar
@@ -39,29 +41,35 @@ Follow instuctions in http://kafka.apache.org/documentation.html#quickstart
     ./gradlew clients:test --tests org.apache.kafka.clients.MetadataTest.testMetadataUpdateWaitTime
 
 ### Running a particular unit test with log4j output ###
-    change the log4j setting in either clients/src/test/resources/log4j.properties or core/src/test/resources/log4j.properties
+Change the log4j setting in either `clients/src/test/resources/log4j.properties` or `core/src/test/resources/log4j.properties`
+
     ./gradlew -i -Dtest.single=RequestResponseSerializationTest core:test
 
 ### Building a binary release gzipped tar ball ###
     ./gradlew clean
     ./gradlew releaseTarGz
-    The above command will fail if you haven't set up the signing key. To bypass signing the artifact, you can run
+
+The above command will fail if you haven't set up the signing key. To bypass signing the artifact, you can run:
+
     ./gradlew releaseTarGz -x signArchives
 
-The release file can be found inside ./core/build/distributions/.
+The release file can be found inside `./core/build/distributions/`.
 
 ### Cleaning the build ###
     ./gradlew clean
 
 ### Running a task on a particular version of Scala (either 2.10.6 or 2.11.7) ###
-#### (If building a jar with a version other than 2.10, need to set SCALA_BINARY_VERSION variable or change it in bin/kafka-run-class.sh to run quick start.) ####
+*Note that if building the jars with a version other than 2.10, you need to set the `SCALA_BINARY_VERSION` variable or change it in `bin/kafka-run-class.sh` to run the quick start.*
+
 You can pass either the major version (eg 2.11) or the full version (eg 2.11.7):
+
     ./gradlew -PscalaVersion=2.11 jar
     ./gradlew -PscalaVersion=2.11 test
     ./gradlew -PscalaVersion=2.11 releaseTarGz
 
 ### Running a task for a specific project ###
-This is for 'core', 'examples' and 'clients'
+This is for `core`, `examples` and `clients`
+
     ./gradlew core:jar
     ./gradlew core:test
 
@@ -69,6 +77,8 @@ This is for 'core', 'examples' and 'clients'
     ./gradlew tasks
 
 ### Building IDE project ####
+*Note that this is not strictly necessary (IntelliJ IDEA has good built-in support for Gradle projects, for example).*
+
     ./gradlew eclipse
     ./gradlew idea
 
@@ -121,6 +131,3 @@ Apache Kafka is interested in building the community; we would welcome any thoug
 
 To contribute follow the instructions here:
  * http://kafka.apache.org/contributing.html
-
-We also welcome patches for the website and documentation which can be found here:
- * https://svn.apache.org/repos/asf/kafka/site