Update README.md

README.md

@@ -84,6 +84,14 @@ cargo build --features debugmozjs
 cargo test --features debugmozjs
 ```
 
+### Create and link prebuilt binary
+
+Spidermonkey is very large which could take a long time to compile. If you are looking for prebuilt version of mozjs, you
+can ask someone to build it and share to you to link it. Mozjs currently offer two environment variables to enable such work:
+
+- `MOZJS_CREATE_MIRROR=1` can create a spidermonkey tarball for release usage.
+- `MOZJS_MIRROR=absolute/path/to/libmozjs.tar.gz` can use this tarball to extract and link the static libraries without compiling spidermonkey and bindgen wrappers.
+
 ### Usage for downstream consumers
 
 Mozjs is currently not published to crates.io, but it can be used from git (binaries should use lockfile instead of `rev`):