fix: invalid documentation link (#2073)

Author: natebwangsut

README.md

@@ -161,7 +161,7 @@ $ ./slsa-verifier-linux-amd64 \
     --tag vX.Y.Z
 ```
 When verification passes, it guarantees that the binary you downloaded was generated using the source code of this repository. 
-If you're interested in reading more about SLSA, visit the official [slsa.dev](slsa.dev).
+If you're interested in reading more about SLSA, visit the official [slsa.dev](https://slsa.dev).
 
 1.  Add the binary to your `GOPATH/bin` directory (use `go env GOPATH` to
     identify your directory if necessary)