Fixes after review by Jane T. and Simon G.

Author: lrineau

Installation/changes.md

@@ -21,7 +21,8 @@ Release date: April 2018
     set to `Release` by default. For a developer using the Visual Studio
     IDE or the Xcode IDE, the change should be transparent. Developers using
     makefiles or the Ninja build-system should set the `CMAKE_BUILD_TYPE`
-    to `Release` manually.
+    to `Release` manually, to avoid using CGAL libraries without any
+    compile-time optimization.
 
 ### 2D Movable Separability of Sets (new package)
 

Maintenance/public_release/announcement/mailing-beta.eml

@@ -11,8 +11,8 @@ a solid ground to report bugs that need to be tackled before the
 release of the final version of CGAL 4.12 in September.
 
 
-*WARNING*: The release features an important change of the CMake scripts
-uses to configure the CGAL libraries and examples. Developers using
+*WARNING*: This release features an important change of the CMake scripts
+used to configure the CGAL libraries and examples. Developers using
 makefiles or the Ninja build-system should set the `CMAKE_BUILD_TYPE` to
 `Release` manually, to avoid using CGAL libraries without any compile-time
 optimization. Please read the first paragraph of the release notes