Add documentation for the Kerberos authentication

[mdumandag]

Added the documentation for the external package we provide
for Kerberos authentication.

[codecov-commenter]

Codecov Report

Merging #453 (1daf053) into master (f05112e) will decrease coverage by 0.24%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #453      +/-   ##
==========================================
- Coverage   94.45%   94.20%   -0.25%     
==========================================
  Files         345      345              
  Lines       17545    17545              
==========================================
- Hits        16572    16529      -43     
- Misses        973     1016      +43     

Impacted Files	Coverage Δ
...otocol/codec/client_authentication_custom_codec.py	50.00% <0.00%> (-23.81%)	⬇️
hazelcast/reactor.py	79.56% <0.00%> (-7.55%)	⬇️
hazelcast/connection.py	91.20% <0.00%> (-1.10%)	⬇️
hazelcast/invocation.py	93.48% <0.00%> (+0.38%)	⬆️
hazelcast/statistics.py	88.62% <0.00%> (+0.59%)	⬆️
hazelcast/proxy/base.py	98.05% <0.00%> (+0.64%)	⬆️
hazelcast/partition.py	90.78% <0.00%> (+1.31%)	⬆️

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[yuce]

Thanks, looks good, except the Kerberos package name.