[Website][Release procedure] missing/not described steps in the procedure

**BUG REPORT**

Release guide and tools are out of sync.
https://bookkeeper.apache.org/community/release_guide/

A few issues that I encountered during 4.13.0 release (not in any particular order) are:

* "Update DC/OS BookKeeper package" step is no longer needed

* site publishing required manual steps not described in the release doc
```
the procedure to publish the new website manually is:

- git clone https://github.com/apache/bookkeeper
- cd bookkeeper/site
- docker/ci.sh
- scripts/publish-website-manually.sh
```

* "Run linux docker container to build release candidate" had a few problems with docker on mac (fixed) plus does not pick up some files from the host machine (i.e. ~/.m2/settings.xml) - some of this might be attributed to the tighter security of teh file system on MacOS Big Sur

Need to describe Docker settings (access to dirs etc)

I had to copy ~/.m2/settings.xml to the docker

`git config --global` step needs the following as well (would be nice to check for this before build starts):
```
git config --global user.email "you@example.com"
git config --global user.name "Your Name"
```
or .gitconfig should be copied to the docker image from the host

Similarly docker didn't have gpg keys, ended up doing `gpg --export-secret-key -a > secretkey.asc` on mac, and copying secretkey.asc into docker, then `gpg --import < secretkey.asc` there

* some steps take *really* long time, i.e. docker build after the tag pushed, and bins to appear at https://archive.apache.org/dist/bookkeeper/ - would be nice to add a warning about that