Updates to bitcoin.html (#187)
Updates to bitcoin.html (#187)

* Updates to bitcoin.html

Adds `rel="noopener"` after every `target="_blank" for improved security and best-practices, and introduces two new high-ranking quality guides for advanced trading category. Also adds "s" to the few "http" urls links so the page contains only secure "https" links.

* Update bitcoin.html

Corrections made in the case of missing spaces between the two characters **"r** in the " target="_blank" rel="noopener", to keep both html elements separate.

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