doc: fix doc for napi_get_value_string_utf8

The API for napi_get_value_string_utf8() appears to have been
previously changed. This improves the doc reflect the current design.

PR-URL: nodejs/node#14529
Fixes: nodejs/node#14398
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

doc/api/n-api.md

@@ -1811,10 +1811,10 @@ NAPI_EXTERN napi_status napi_get_value_string_latin1(napi_env env,
 - `[in] value`: `napi_value` representing JavaScript string.
 - `[in] buf`: Buffer to write the ISO-8859-1-encoded string into. If NULL is
 passed in, the length of the string (in bytes) is returned.
-- `[in] bufsize`: Size of the destination buffer.
-- `[out] result`: Number of bytes copied into the buffer including the null
-terminator. If the buffer size is insufficient, the string will be truncated
-including a null terminator.
+- `[in] bufsize`: Size of the destination buffer. When this value is
+insufficient, the returned string will be truncated.
+- `[out] result`: Number of bytes copied into the buffer, excluding the null
+terminator.
 
 Returns `napi_ok` if the API succeeded. If a non-String `napi_value`
 is passed in it returns `napi_string_expected`.
@@ -1837,11 +1837,11 @@ napi_status napi_get_value_string_utf8(napi_env env,
 - `[in] env`: The environment that the API is invoked under.
 - `[in] value`: `napi_value` representing JavaScript string.
 - `[in] buf`: Buffer to write the UTF8-encoded string into. If NULL is passed
-in, the length of the string (in bytes) is returned.
-- `[in] bufsize`: Size of the destination buffer.
-- `[out] result`: Number of bytes copied into the buffer including the null
-terminator. If the buffer size is insufficient, the string will be truncated
-including a null terminator.
+ in, the length of the string (in bytes) is returned.
+- `[in] bufsize`: Size of the destination buffer. When this value is
+insufficient, the returned string will be truncated.
+- `[out] result`: Number of bytes copied into the buffer, excluding the null
+terminator.
 
 Returns `napi_ok` if the API succeeded. If a non-String `napi_value`
 is passed in it returns `napi_string_expected`.
@@ -1864,10 +1864,10 @@ napi_status napi_get_value_string_utf16(napi_env env,
 - `[in] value`: `napi_value` representing JavaScript string.
 - `[in] buf`: Buffer to write the UTF16-LE-encoded string into. If NULL is
 passed in, the length of the string (in 2-byte code units) is returned.
-- `[in] bufsize`: Size of the destination buffer.
-- `[out] result`: Number of 2-byte code units copied into the buffer including
-the null terminator. If the buffer size is insufficient, the string will be
-truncated including a null terminator.
+- `[in] bufsize`: Size of the destination buffer. When this value is
+insufficient, the returned string will be truncated.
+- `[out] result`: Number of 2-byte code units copied into the buffer, excluding the null
+terminator.
 
 Returns `napi_ok` if the API succeeded. If a non-String `napi_value`
 is passed in it returns `napi_string_expected`.