Add PEM Key passphrase removal instructions

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PEM pass phrase: Prompt

The PEM pass phrase: prompt can be the result of using an encrypted (password-protected) PYTAK_TLS_CLIENT_KEY file. Depending on the security requirements in your operating environment,

is the result of using an encrypted (password-protected) PYTAK_TLS_CLIENT_KEY, in your case /etc/pytak.key. You're correct that it's the default TAK Server CoreConfig password. You can avoid the PEM pass phrase: prompt by removing the password protection from the PYTAK_TLS_CLIENT_KEY using the instructions here:

openssl rsa -in pytak.key -out pytak.nopass.key