Add release note for the -S and -B options.

Help/release/dev/cmake-explicit-dirs.rst

@@ -0,0 +1,10 @@
+cmake-explicit-dirs
+-------------------
+
+* The :manual:`cmake <cmake(1)>` command gained the ``-S <source_dir>``
+  command line option to specify the location of the source directory.
+  This option can be used independently of ``-B``.
+
+* The :manual:`cmake <cmake(1)>` command gained the ``-B <build_dir>``
+  command line option to specify the location of the build directory.
+  This option can be used independently of ``-S``.