README: Note other side-channel and fault attacks are currently out of scope

Signed-off-by: Matthias J. Kannwischer <matthias@zerorisc.com>

Author: mkannwischer

README.md

@@ -80,6 +80,8 @@ through suitable barriers and constant-time patterns.
 Absence of secret-dependent branches, memory-access patterns and variable-latency instructions is also tested using `valgrind`
 with various combinations of compilers and compilation options.
 
+**Other attacks.** mlkem-native targets resistance against timing side-channels only. Other attack classes, such as power and electromagnetic side-channels, microarchitectural side-channels (e.g. speculative execution), or fault-injection attacks, are currently out of scope.
+
 ## Design
 
 mlkem-native is split into a _frontend_ and two _backends_ for arithmetic and FIPS202 / SHA3. The frontend is