Added validation tool and docs

doc/Support/Install Validation.md

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+Install validation
+------------------
+
+With a lot of configuration possibilities and at present the only way to do this being by manually editing config.php then it's not 
+uncommon that mistakes get made. It's also impossible to validate user input in config.php when you're just using a text editor :)
+
+So, to try and help with some of the general issues people come across we've put together a simple validation tool which at present will: 
+
+ - Validate config.php from a php perspective including whitespace where it shouldn't be.
+ - Connection to your MySQL server to verify credentials.
+ - Checks if you are running the older alerting system.
+ - Checks your rrd directory setup if not running rrdcached.
+ - Checks disk space for where /opt/librenms is installed.
+
+Optionally you can also pass -m and a module name for that to be tested. Current modules are:
+
+ - mail. This will validate your mail transport configuration.
+
+Output, this is color coded to try and make things a little easier:
+
+Green OK - This is a good thing, you can skip over these :)
+
+Yellow WARN - You probably want to check this out.
+
+Red FAIL - This is going to need your attention!