## Issue Addressed
https://github.com/sigp/lighthouse/issues/2889
## Additional Info
I have checked that linkcheck has succeeded on the book built locally. 👌
```shell
$ cd book
$ mdbook serve --open
...
2022-01-14 01:13:40 [INFO] (mdbook::book): Book building has started
2022-01-14 01:13:40 [INFO] (mdbook::book): Running the html backend
$ linkcheck http://localhost:3000
Perfect. Checked 4495 links, 80 destination URLs (76 ignored).
```
Also I'll tackle running linkcheck on CI in another pull request.
## Issue Addressed
NA
## Proposed Changes
Updates the validator guide to provide instructions for mainnet users.
## Additional Info
- ~~Blocked on #1751~~
## Issue Addressed
NA
## Proposed Changes
Adds support for using the [`cross`](https://github.com/rust-embedded/cross) project to produce cross-compiled binaries using Docker images.
Provides quite clean and simple cross-compiles cause all the complexity is hidden in Dockerfiles. It does require you to be in the `docker` group though.
## Details
- Adds shortcut commands to `Makefile`
- Ensures `reqwest` and `discv5` use vendored openssl libs (i.e., static not shared).
- Switches to a [commit](284f705964) of blst that has a renamed C function to avoid a collision with openssl (upstream issue: https://github.com/supranational/blst/issues/21).
- Updates `ring` to the latest satisfiable version, since an earlier version was causing issues with `cross`.
- Off-topic, but adds extra message about Windows support as suggested by Discord user.
## Additional Info
- ~~Blocked on #1495~~
- There are no tests in CI for this yet for a few reasons:
- I'm hesitant to add more long-running tasks.
- Short-term bitrot should be avoided since we'll use it each release.
- In the long term I think it would be good to automate binary creation on a release.
- I observed the binaries increase in size from 50mb to 52mb after these changes.
