add note on uint64 string conversion

Author: JoshuaMoelans

platform-includes/performance/improving-data/native.mdx

@@ -2,7 +2,8 @@
 You can add Data Attributes to both Spans and Transactions. This data is visible in the trace explorer in Sentry.
 The data must be of type `sentry_value_t`, which can store:
 * 32-bit signed integers,
-* 64-bit signed and unsigned integers,
+* 64-bit signed integers,
+* 64-bit unsigned integers (due to a current limitation in processing, these will be converted to strings before sending),
 * double-precision floating-points,
 * null-terminated strings, as well as
 * lists and string-keyed maps containing `sentry_value_t` entries