Add bold letter warning to Readme that this has dangerous side effects

[kellyselden]

Relating to #41.

I tried to add this to a single spot in a large app to get fragment identifiers working. I didn't realize it was causing 404s in various locations because we still have some server rendered pages that are linked to, and we have a catchall route.
I didn't realize the initializer was handling all links, not just the one's I was modifying.

[danwenzel]

Opened a PR to address this: #124