[MNG-8011] Neuter the README (#1470)

The site already contains all the required information, point user at it. It would be insane for us to maintain all these information here as well (as example shows, it was totally outdated).

Keep it short, and just keep pointers to proper info sources.

---

https://issues.apache.org/jira/browse/MNG-8011

apache-maven/README.txt

@@ -16,50 +16,12 @@
   Release Notes
   -------------
 
-  The full list of changes can be found at https://maven.apache.org/docs/history.html.
-
-  System Requirements
-  -------------------
-
-  JDK:
-    8 or above (this is to execute Maven - it still allows you to build against 1.3
-    and prior JDK's).
-  Memory:
-    No minimum requirement.
-  Disk:
-    Approximately 10MB is required for the Maven installation itself. In addition to
-    that, additional disk space will be used for your local Maven repository. The size
-    of your local repository will vary depending on usage but expect at least 500MB.
-  Operating System:
-    Windows:
-      Windows 2000 or above.
-    Unix based systems (Linux, Solaris and Mac OS X) and others:
-      No minimum requirement.
+  The full list of changes, system requirements and related can be found at https://maven.apache.org/docs/history.html.
 
   Installing Maven
   ----------------
 
-  1) Unpack the archive where you would like to store the binaries, e.g.:
-
-    Unix-based operating systems (Linux, Solaris and Mac OS X)
-      tar zxvf apache-maven-3.x.y.tar.gz
-    Windows
-      unzip apache-maven-3.x.y.zip
-
-  2) A directory called "apache-maven-3.x.y" will be created.
-
-  3) Add the bin directory to your PATH, e.g.:
-
-    Unix-based operating systems (Linux, Solaris and Mac OS X)
-      export PATH=/usr/local/apache-maven-3.x.y/bin:$PATH
-    Windows
-      set PATH="c:\program files\apache-maven-3.x.y\bin";%PATH%
-
-  4) Make sure JAVA_HOME is set to the location of your JDK
-
-  5) Run "mvn --version" to verify that it is correctly installed.
-
-  For complete documentation, see https://maven.apache.org/download.html#Installation
+  For complete documentation see https://maven.apache.org/download.html#Installation
 
   Licensing
   ---------