Ensure that GitHub's "View license" link points to complete license info for all our repos

[daira]

GitHub's "View license" link can only point to one file. For example, if there is LICENSE-APACHE and LICENSE-MIT but no COPYRIGHT or COPYING, it will point to LICENSE-APACHE. This is misleading because it disregards the MIT licensing option.

Here are examples of dual MIT/Apache repos where the "View license" link points to a file with complete license info:

• https://github.com/rust-lang/rust (points to COPYRIGHT)
• https://github.com/zcash/zcash (points to COPYING)

Dual-licensed repos that this affects:

• [x] https://github.com/zcash/librustzcash/pull/449
• [x] https://github.com/zcash/incrementalmerkletree/pull/8
• [x] https://github.com/zcash/pasta_curves/pull/23
• [x] https://github.com/zcash-hackworks/zcash-test-vectors/pull/53
  • [x] updated in https://github.com/zcash-hackworks/zcash-test-vectors/pull/60
• [x] https://github.com/zcash-hackworks/bn/pull/23

Other repos with no or unrecognized license information:

• [ ] https://github.com/zcash-hackworks/zcash-testnet-in-a-box [should be MIT/Apache]
• [ ] https://github.com/zcash/mpc [should be MIT/Apache]
• [ ] https://github.com/zcash/zcash-gitian [should be MIT/Apache]
• [ ] https://github.com/zcash/gitian.sigs [should be MIT/Apache]
• [ ] https://github.com/zcash/sapling-security-analysis [should be MIT/Apache]
• [ ] https://github.com/zcash/developers [should be MIT/Apache]
• [ ] https://github.com/zcash/zcash-seeder (forked from https://github.com/sipa/bitcoin-seeder which also has unclear licensing)
• [ ] https://github.com/zcash/zeclink [deleted, but shouldn't have been?]
• [ ] https://github.com/zcash/homebrew-formulae
• [ ] https://github.com/zcash/zcash-blog
• [ ] https://github.com/zcash/zcash-gitcoin (basically empty)
• [ ] https://github.com/zcash/zcash-wordpress-theme

[daira]

Review needed for https://github.com/zcash-hackworks/zcash-test-vectors/pull/53; if that is okay then I'll file similar PRs for the other four MIT/Apache repos.