docs: verify and reproduce builds (#6515)

* docs/REPRODUCIBLE: add new

* docs/REPRODUCIBLE: clarify Android requirements

* rename to REPRODUCE

* expand and fix sections

* website

* docs, site: change links to simplex.apk to simplex-aarch64.apk

---------

Co-authored-by: Evgeny Poberezkin <evgeny@poberezkin.com>

website/src/_data/docs_sidebar.json

@@ -28,6 +28,7 @@
                 "WEBRTC.md",
                 "XFTP-SERVER.md",
                 "DOWNLOADS.md",
+                "REPRODUCE.md",
                 "TRANSPARENCY.md",
                 "SECURITY.md",
                 "FAQ.md"