Add update and changelog files

changelog.md

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+Telegram channel:
+https://t.me/playintegrityfix
+
+Device verdict should pass by default.
+If not, try removing /data/adb/pif.json file.
+
+Donations:
+https://www.paypal.com/paypalme/chiteroman
+
+# v16.6
+
+- Change fingerprint to fix RCS
+- Misc improvements

update.json

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+{
+  "version": "v16.6",
+  "versionCode": 16600,
+  "zipUrl": "https://github.com/chiteroman/PlayIntegrityFix/releases/download/v16.6/PlayIntegrityFix_v16.6.zip",
+  "changelog": "https://raw.githubusercontent.com/chiteroman/PlayIntegrityFix/main/changelog.md"
+}