Clearer build and install instructions in the README file for Github users.

Fixes #634.

Doc/Manual/Preface.html

@@ -265,6 +265,12 @@ the main SWIG distribution. There is no need to download anything else.
 
 <H3><a name="Preface_unix_installation">1.12.2 Unix installation</a></H3>
 
+<p>
+These installation instructions are for using the distributed tarball,
+for example, <tt>swig-3.0.8.tar.gz</tt>.
+If you wish to build and install from source on Github, extra steps are required.
+Please see the <a href="http://swig.org/svn.html">Bleeding Edge</a> page on the SWIG website.
+</p>
 
 <p>
 You must use <a href="http://www.gnu.org/software/make/">GNU make</a> to build and install SWIG.

README

@@ -68,9 +68,13 @@ than one version of SWIG.
 Installation
 ============
 Please read the Doc/Manual/Preface.html#Preface_installation for
-full installation instructions for Windows, Unix and Mac OS X.
+full installation instructions for Windows, Unix and Mac OS X
-The INSTALL file has generic build and installation instructions for
+using the release tarball/zip file. The INSTALL file has generic
-Unix users.
+build and installation instructions for Unix users.
+Users wishing to build and install code from Github should
+visit http://swig.org/svn.html to obtain the more detailed
+instructions required for building code obtained from Github - extra
+steps are required compared to building from the release tarball.
 
 Testing
 =======