upd: DNSCrypt url fixed.

[ramazansancar]

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What does this PR aim to accomplish?:
Added Archive.org link to removed link.

How does this PR accomplish the above?:
By giving the right guidance

Link documentation PRs if any are needed to support this PR:
https://github.com/DNSCrypt/dnscrypt-proxy/wiki/Installation-linux

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[yubiuser]

I think the right solution is not to link to an archive version of an removed wiki article (which are probably outdated already - last edited 2018/19) but to port the stored (and updated) information to the doc

[ramazansancar]

The Internet archive was inaccessible. So this method didn't make sense anymore. At least for a while. @yubiuser

[rdwebdesign]

The original wiki pages were removed because they were really outdated (last update was 2016 or 2018).
Pointing these links to web archive (outdated content) is a bad idea.

I see 3 solutions:

1. replace the old links with more current references to DNSCrypt (if there are good references);
2. completely rewrite Alternatives section (maybe using different solutions) and include up-to-date references;
3. completely remove the Alternatives section.

Personally I think the last option would be better.