This PR adds a symbolic link to the top-level LICENSE file in libcramjam/, which ensures that a license file appears in the published crate as required by the chosen MIT license terms.

Before this PR:

gh repo clone milesgranger/cramjam
cd cramjam/libcramjam
git checkout add-c-api
cargo publish --dry-run
tar -tzvf ../target/package/libcramjam-0.1.5.crate

(no license file appears in the output)

After this PR:

[…]
-rw-r--r-- 0/0            1070 2006-07-23 21:21 libcramjam-0.1.5/LICENSE
[…]

Note that the symbolic link is resolved by cargo publish, and a regular file appears in the crate.