Fixed #12092 -- Fixed grammar error in install.txt. Thanks, Abizern and timo

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12169 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/intro/install.txt

@@ -71,11 +71,11 @@ You've got three easy options to install Django:
       
 .. warning::
 
-    If do either of the first two steps, keep an eye out for parts of the
+    If you do either of the first two steps, keep an eye out for parts of the
     documentation marked **new in development version**. That phrase flags
-    features that are only available in development versions of Django; if you
-    try to use them with an official release they won't work.
-    
+    features that are only available in development versions of Django, and
+    they likely won't work with an official release.
+
 That's it!
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