Add license type: MIT+BSD are NOTICE licenses

Also contains a warning that linking the wrong way can entangle GPL
code, but let's assume we heed the warning and link the right way.

Bug: 68860345
Bug: 69058154
Bug: 151953481

Test: no code changes
Change-Id: I712e2a5182f01d30fd0629ab6cf08702cb25fed1
diff --git a/METADATA b/METADATA
index 334588f..2c65095 100644
--- a/METADATA
+++ b/METADATA
@@ -10,6 +10,7 @@
     value: "ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre2-10.33.zip"
   }
   version: "10.33"
+  license_type: NOTICE
   last_upgrade_date {
     year: 2019
     month: 8