Mess with the Encryption section

The Encryption section in the matrix documentation shows some strange behavior, which is apparently caused by some js manipulation of the site.

When loading https://matrix.org/docs/develop/ freshly, the link to article _'End-to-End Encryption implementation guide'_ is wrong and points to https://matrix.org/docs/guides/implementing-stateres instead.

After clicking an arbitrary article and navigating back via the browser's return function, the link surprisingly is fixed and points to https://matrix.org/docs/guides/end-to-end-encryption-implementation-guide as it should. But now, the Encryption section has a duplicate _'An introduction to end-to-end encryption in Matrix and Riot'_ entry. With each repetition, a new such entry gets appended.

Tried this in Firefox, both with Linux and Android.

Reproduce the issue on https://matrix.org/docs/develop/ in Firefox by loading the page, opening an arbitrary article, and navigating back. Inspect the JavaScript manipulation of the Encryption section and verify that the implementation-guide link remains correct and that the introduction entry is not appended repeatedly.

Written by the indexing model from the issue text.