Docs: Added some docs explaining how to update mkdocs.

3 jobs for master in 2 minutes and 38 seconds (queued for 3 seconds)
Name Stage Failure
failed
pages Deploy
    data = constructor(self, tag_suffix, node)
File "/usr/local/lib/python3.5/site-packages/yaml/constructor.py", line 537, in construct_python_name
return self.find_python_name(suffix, node.start_mark)
File "/usr/local/lib/python3.5/site-packages/yaml/constructor.py", line 524, in find_python_name
"cannot find module %r (%s)" % (module_name, exc), mark)
yaml.constructor.ConstructorError: while constructing a Python object
cannot find module 'pymdownx.emoji' (No module named 'pymdownx')
in "/builds/Ferma/Ferma/mkdocs.yml", line 53, column 24
ERROR: Job failed: exit code 1