Fix trivial typo in Readme (GH-2185)

Replace platform with platforms.

diff --git a/Doc/using/index.rst b/Doc/using/index.rst
index a5df713944cc5d55bc50e052dfbd6081658affb1..4f0aa7d9577df6fb1398f4d0c34095b3d935d588 100644 (file)
--- a/Doc/using/index.rst
+++ b/Doc/using/index.rst
@@ -6,7 +6,7 @@
 
 
 This part of the documentation is devoted to general information on the setup
-of the Python environment on different platform, the invocation of the
+of the Python environment on different platforms, the invocation of the
 interpreter and things that make working with Python easier.