doc: version: document the numeric version limits

The `VERSION` numeric fields are used to construct the `uint32_t`
`KERNELVERSION` and `APPVERSION` values, which only allocates a single
byte for each field.

The field in `app_version.h` is `APP_TWEAK`, not `APP_VERSION_TWEAK`.

Signed-off-by: Jordan Yates <jordan@embeint.com>

doc/build/version/index.rst

@@ -34,20 +34,21 @@ a newline. The basic ``VERSION`` file has the following structure:
  VERSION_TWEAK =
  EXTRAVERSION =
 
-Each field and the values it supports is described below (note that there may be further
-restrictions depending upon what the version is used for, e.g. bootloaders might only support some
-of these fields or might place limits on the maximum values of fields):
+Each field and the values it supports is described below. Zephyr limits the value of each numeric
+field to a single byte (note that there may be further restrictions depending upon what the version
+is used for, e.g. bootloaders might only support some of these fields or might place limits on the
+maximum values of fields):
 
 +---------------+----------------------------------------+
 | Field | Data type |
 +---------------+----------------------------------------+
-| VERSION_MAJOR | Numerical   |
+| VERSION_MAJOR | Numerical (0-255) |
 +---------------+----------------------------------------+
-| VERSION_MINOR | Numerical   |
+| VERSION_MINOR | Numerical (0-255) |
 +---------------+----------------------------------------+
-| PATCHLEVEL | Numerical   |
+| PATCHLEVEL | Numerical (0-255) |
 +---------------+----------------------------------------+
-| VERSION_TWEAK | Numerical   |
+| VERSION_TWEAK | Numerical (0-255) |
 +---------------+----------------------------------------+
 | EXTRAVERSION | Alphanumerical (Lowercase a-z and 0-9) |
 +---------------+----------------------------------------+
@@ -91,7 +92,7 @@ following defines are available:
 +-----------------------------+-------------------+------------------------------------------------------+-------------------------+
 | APP_PATCHLEVEL | Numerical | ``PATCHLEVEL`` | 3 |
 +-----------------------------+-------------------+------------------------------------------------------+-------------------------+
-| APP_VERSION_TWEAK | Numerical | ``VERSION_TWEAK`` | 4 |
+| APP_TWEAK  | Numerical | ``VERSION_TWEAK`` | 4 |
 +-----------------------------+-------------------+------------------------------------------------------+-------------------------+
 | APP_VERSION_STRING | String (quoted) | ``VERSION_MAJOR``, |br| | "1.2.3-unstable" |
 | | | ``VERSION_MINOR``, |br| | |