add help for check_ssl

docs/20_Checks/check_ssl.md

+## Check ssl
+
+Script: `check_ssl`
+
+**check_ssl_certs** is a plugin to check an ssl connection to a host on given port.
+
+## Requirements
+
+* openssl client
+
+## Standalone installation
+
+From this repository ypu need next to this script:
+
+* `inc_pluginfunctions` shared function for all IML checks written in bash
+
+## Syntax
+
+Start the script without params to get the help.
+
+```txt
+______________________________________________________________________
+
+CHECK_SSL
+v1.4
+
+(c) Institute for Medical Education - University of Bern
+Licence: GNU GPL 3
+
+https://os-docs.iml.unibe.ch/icinga-checks/Checks/check_ssl.html
+______________________________________________________________________
+
+Check if ssl certificate of a given domain is still valid.
+You can check https or any other port of a ssl enabled service like LDAPS, 
+IMPAS and others.
+
+You can customize the values for warning and critical level.
+
+SYNTAX: check_ssl [options] DOMAIN [PORT]
+
+OPTIONS
+    -w VALUE  warning level for expiration in days (default: 28)
+    -c VALUE  critical level for expiration in days (default: 7)
+
+PARAMETERS
+    DOMAIN    domain to verify the ssl vertificate from (required)
+    PORT      optional: port number to connect (default: 443)
+
+
+EXAMPLES
+
+    check_ssl www.iml.unibe.ch 443
+        check https port 443
+
+    check_ssl -w 30 -c 14 ldap.example.com 636
+        check ldaps port 636 and set custom warning and critical level
+
+```
+
+## Examples
+
+### Check Website with https
+
+To check a domain name on port 443 add the domain to connect as parameter. The port number 443 is default and not needed.
+
+```txt
+./check_ssl www.iml.unibe.ch
+OK: www.iml.unibe.ch:443 - valid to Apr 23 00:38:13 2025 GMT (69 days left)
+```
+
+### Check Ldaps
+
+```txt
+./check_ssl ldap.example.com 636
+OK: ldap.example.com:636 - valid to Apr  6 00:44:42 2025 GMT (52 days left)
+```