Created Synology RT1900ac install guide (markdown)

Synology-RT1900ac-install-guide.md

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+I got tired of manually maintaining Let's Encrypt on my laptop to update my Router.
+so I now pushed that to the router itself.
+
+here's the HowTo (xpost https://forum.synology.com/enu/viewtopic.php?f=265&t=123003 ).
+I've used https://github.com/Neilpang/acme.sh , a 3rd party client for Let's Encrypt, based on Perl. no extra dependencies.
+I've also used it with DNS01 protocol, which means, I don't have any ports open on the router to do the validation, instead it use Cloudflare API, where I host my domain.
+
+Since the Router shell is very limited, there are several constraints. the most important of all, there is no cron/crontab.
+
+trying the default install
+$ wget -O -  https://get.acme.sh | sh
+, will fail cause of cron. 
+
+so we have to do it manually
+$ wget https://github.com/Neilpang/acme.sh/archive/master.tar.gz
+$ tar xvf master.tar.gz
+$ cd acme.sh-master/
+$ ./acme.sh --install --nocron
+
+so install is done :)
+
+next, config
+$ cd ~/.acme.sh/
+$ vi  acme.sh account.conf 
+set your email, cloudflare account and API (https://www.cloudflare.com/a/account/my-account)
+ctrl+c 
+:wq (and you are out of VI(M)
+
+now to create your cert
+$ ./acme.sh  --issue -d YOURDOMAIN.TLD --dns dns_cf --certpath /usr/syno/etc/ssl/ssl.crt/server.crt --keypath /usr/syno/etc/ssl/ssl.key/server.key --fullchainpath /
+usr/syno/etc/ssl/ssl.intercrt/server-ca.crt
+(anyone knows how to restart the webserver?)
+
+simple right?
+
+since there is no cron, the renewal still requires manual work.
+
+I've added this line at the bottom of /etc/rc and ~/.profile
+/root/.acme.sh/acme.sh --cron
+so when the router is rebooted or you ssh into it, it tries to renew the cert.
+
+HTH