Add documentation TransIP DNS TXT usage

[Erriez]

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:

Add documentation TransIP DNS plugin file /swag/config/dns-conf/transip.ini.

Benefits of this PR and context:

The original text in the transip.ini file was unclear. I was not able to generate a wildcard certificate by insufficient instructions in the comments and documentation URL. Finally I discovered that the transip.key is a TransIP API key pair. Then it was very easy to use this plugin.

How Has This Been Tested?

No source changes made, only comments added. Log:

swag             | Using Let's Encrypt as the cert provider
swag             | SUBDOMAINS entered, processing
swag             | Wildcard cert for mydomain.nl will be requested
swag             | E-mail address entered: removed@mydomain.nl
swag             | dns validation via transip plugin is selected
swag             | Generating new certificate
swag             | Saving debug log to /var/log/letsencrypt/letsencrypt.log
swag             | Plugins selected: Authenticator dns-transip, Installer None
swag             | Requesting a certificate for *.mydomain.nl and mydomain.nl
swag             | Performing the following challenges:
swag             | dns-01 challenge for mydomain.nl
swag             | dns-01 challenge for mydomain.nl
swag             | Unsafe permissions on credentials configuration file: /config/dns-conf/transip.ini
swag             | Successfully added TXT record
swag             | Successfully added TXT record
swag             | Waiting 240 seconds for DNS changes to propagate
swag             | Waiting for verification...
swag             | Cleaning up challenges
swag             | Removing TXT record with name: _acme-challenge
swag             | Removing TXT record with name: _acme-challenge
swag             | IMPORTANT NOTES:
swag             |  - Congratulations! Your certificate and chain have been saved at:
swag             |    /etc/letsencrypt/live/mydomain.nl/fullchain.pem
swag             |    Your key file has been saved at:
swag             |    /etc/letsencrypt/live/mydomain.nl/privkey.pem
swag             |    Your certificate will expire on 2021-05-05. To obtain a new or
swag             |    tweaked version of this certificate in the future, simply run
swag             |    certbot again. To non-interactively renew *all* of your
swag             |    certificates, run "certbot renew"
swag             |  - If you like Certbot, please consider supporting our work by:
swag             | 
swag             |    Donating to ISRG / Let's Encrypt:   https://letsencrypt.org/donate
swag             |    Donating to EFF:                    https://eff.org/donate-le
swag             | 
swag             | New certificate generated; starting nginx
swag             | Starting 2019/12/30, GeoIP2 databases require personal license key to download. Please retrieve a free license key from MaxMind,
swag             | and add a new env variable "MAXMINDDB_LICENSE_KEY", set to your license key.
swag             | [cont-init.d] 50-config: exited 0.
swag             | [cont-init.d] 60-renew: executing... 
swag             | The cert does not expire within the next day. Letting the cron script handle the renewal attempts overnight (2:08am).
swag             | [cont-init.d] 60-renew: exited 0.
swag             | [cont-init.d] 70-templates: executing... 
swag             | [cont-init.d] 70-templates: exited 0.
swag             | [cont-init.d] 99-custom-files: executing... 
swag             | [custom-init] no custom files found exiting...
swag             | [cont-init.d] 99-custom-files: exited 0.
swag             | [cont-init.d] done.
swag             | [services.d] starting services
swag             | [services.d] done.
swag             | nginx: [alert] detected a LuaJIT version which is not OpenResty's; many optimizations will be disabled and performance will be compromised (see https://github.com/openresty/luajit2 for OpenResty's LuaJIT or, even better, consider using the OpenResty releases from https://openresty.org/en/download.html)
swag             | Server ready

Source / References:

N.A.

Closes #82

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[LinuxServer-CI]

I am a bot, here are the test results for this PR:
https://ci-tests.linuxserver.io/lspipepr/swag/1.12.0-pkg-f63d4034-pr-69/index.html
https://ci-tests.linuxserver.io/lspipepr/swag/1.12.0-pkg-f63d4034-pr-69/shellcheck-result.xml

[LinuxServer-CI]

I am a bot, here are the test results for this PR:
https://ci-tests.linuxserver.io/lspipepr/swag/1.12.0-pkg-28f8abba-pr-69/index.html
https://ci-tests.linuxserver.io/lspipepr/swag/1.12.0-pkg-28f8abba-pr-69/shellcheck-result.xml