Fix trivial typos in text

Some are user facing.

Found using

    codespell -q 3 --skip="./Utilities" -I .cmake-whitelist.txt`

whereby the whitelist contained:

    ans
    dum
    helpfull
    emmited
    emmitted
    buil
    iff
    isnt
    nto
    ot
    pathes
    substract
    te
    todays
    upto
    whitespaces

Help/command/add_subdirectory.rst

@@ -30,7 +30,7 @@ project that is useful but not necessary, such as a set of examples.
 Typically the subdirectory should contain its own :command:`project`
 command invocation so that a full build system will be generated in the
 subdirectory (such as a VS IDE solution file).  Note that inter-target
-dependencies supercede this exclusion.  If a target built by the
+dependencies supersede this exclusion.  If a target built by the
 parent project depends on a target in the subdirectory, the dependee
 target will be included in the parent project build system to satisfy
 the dependency.

Help/command/file.rst

@@ -110,7 +110,7 @@ regular expressions, but much simpler.  If ``RELATIVE`` flag is
 specified, the results will be returned as relative paths to the given
 path.  The results will be ordered lexicographically.
 
-By default ``GLOB`` lists directories - directories are omited in result if
+By default ``GLOB`` lists directories - directories are omitted in result if
 ``LIST_DIRECTORIES`` is set to false.
 
 .. note::

Help/command/install.rst

@@ -346,7 +346,7 @@ specified that does not match that given to the targets associated with
 included in the export but a target to which it links is not included
 the behavior is unspecified.
 
-In additon to cmake language files, the ``EXPORT_ANDROID_MK`` option maybe
+In addition to cmake language files, the ``EXPORT_ANDROID_MK`` option maybe
 used to specifiy an export to the android ndk build system.  The Android
 NDK supports the use of prebuilt libraries, both static and shared. This
 allows cmake to build the libraries of a project and make them available