doc: services: logging: Clarify limitations

Add note about limitation regarding logging strings with width. Clarify
that it is required to cast character pointer to non-character pointer
when used with %p format specifier.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

doc/services/logging/index.rst

@@ -758,8 +758,8 @@ Please refer to the :zephyr:code-sample:`logging-dictionary` sample to learn mor
 the log parser.
 
 
-Recommendations
-***************
+Recommendations and limitations
+*******************************
 
 The are following recommendations:
 
@@ -771,7 +771,7 @@ The are following recommendations:
   format specifier and it points to a constant string.
 * It is recommended to cast pointer to ``char *`` when it is used with ``%s``
   format specifier and it points to a transient string.
-* It is recommended to cast character pointer to non character pointer
+* It is required to cast a character pointer to non character pointer
   (e.g., ``void *``) when it is used with ``%p`` format specifier.
 
 .. code-block:: c
@@ -779,6 +779,11 @@ The are following recommendations:
    LOG_WRN("%s", str);
    LOG_WRN("%p", (void *)str);
 
+There are following limitations:
+
+* Logging does not support string format specifier with width (e.g., ``%.*s`` or ``%8s``). That
+  is because format string content is not used to build a log message, only argument types.
+
 Benchmark
 *********