docs: add missing system content from components.xml

The DocBook version of the Beaker Guide contained a file components.xml,
which was not referenced in the actual book and was mostly duplicate
content. It did have a few useful bits which belong on the Systems page
however.

This content is rescued from pub_doc/Beaker_Guide/en-US/components.xml
in commit bf25a01e.

Change-Id: I256320da751c3bbb0a4d6c4f232abc5683668d1f
docs: missed converting one HTML admonition

Change-Id: I9db8cb2248c2c72250372d1fd4486f79ab63032d
docs: fix a bunch of spelling errors

Change-Id: I2be6c6ec1547cf2c528134795935608cf7370c7a