IMPALA-10144 Add a statement of platforms that Impala runs on

Now Impala can run on arm64 platform, this adds a
statement of platforms Impala runs on.

Change-Id: I009396bef9faa3b7d686559324127bf1daea5e73
Reviewed-on: http://gerrit.cloudera.org:8080/16415
Reviewed-by: Tim Armstrong <tarmstrong@cloudera.com>
Tested-by: Tim Armstrong <tarmstrong@cloudera.com>
diff --git a/README.md b/README.md
index 7faa653..5adf7c0 100644
--- a/README.md
+++ b/README.md
@@ -34,6 +34,9 @@
 ## Supported Platforms
 
 Impala only supports Linux at the moment.
+Impala supports x86_64 and has experimental support for arm64 (as of Impala 4.0).
+[Impala Requirements](https://impala.apache.org/docs/build/html/topics/impala_prereqs.html)
+contains more detailed information on the minimum CPU requirements.
 
 ## Export Control Notice