add a small note describing what proj.4 is

OSGeo · Mar 3, 2016 · 51fa20d · 51fa20d
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commit 51fa20d
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diff --git a/docs/source/index.rst b/docs/source/index.rst
@@ -4,6 +4,11 @@
 proj.4
 ******************************************************************************
 
+proj.4 is a standard Unix filter function which converts geographic longitude
+and latitude coordinates into cartesian coordinates (and vice versa), and it is
+a C API for software developers to include coordinate transformation in their
+own software.
+
 
 =============  ================================================================
  Platform                Test Status and Coverage