[docs][clang] Add extra information inside -fsanitize=unsigned-shift-base for UndefinedBehaviorSanitizer

[aabhinavg]

Summary

Close: #60712

[Eugene.Zelenko]

clang/docs/UndefinedBehaviorSanitizer.rst

160–161

Missing space after period.

[aabhinavg]

Done minor fix.

[MaskRay]

Thanks!

clang/docs/UndefinedBehaviorSanitizer.rst

Available checks are:
   -  ``-fsanitize=shift``: Shift operators where the amount shifted is
      greater or equal to the promoted bit-width of the left hand side
      or less than zero, or where the left hand side is negative. For a
      signed left shift, also checks for signed overflow in C, and for
      unsigned overflow in C++. You can use ``-fsanitize=shift-base`` or
      ``-fsanitize=shift-exponent`` to check only left-hand side or
      right-hand side of shift operation, respectively.
   -  ``-fsanitize=unsigned-shift-base``: check that an unsigned left-hand side of
-     a left shift operation doesn't overflow.
+     a left shift operation doesn't overflow. Issues caught by this sanitizer are 
+     not undefined behavior, but are often unintentional.
   -  ``-fsanitize=signed-integer-overflow``: Signed integer overflow, where the
      result of a signed integer computation cannot be represented in its type.
      This includes all the checks covered by ``-ftrapv``, as well as checks for
      signed division overflow (``INT_MIN/-1``), but not checks for
      lossy implicit conversions performed before the computation
      (see ``-fsanitize=implicit-conversion``). Both of these two issues are
      handled by ``-fsanitize=implicit-conversion`` group of checks.
   -  ``-fsanitize=unreachable``: If control flow reaches an unreachable