Update docs to fix local-tld config path for custom Node installation

I was on IRC earlier asking about an issue where `hoodie start` would time out as `hoodie` could not locate the DB. I've managed to track the issue down to an incorrect Node path set in `~/Library/LaunchAgents/ie.hood.local-tld-service.plist`.

The file originally looked like this:

```
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Label</key>
        <string>ie.hood.local-tld-service</string>
        <key>ProgramArguments</key>
        <array>
                <string>/usr/local/bin/node</string>
                <string>/Users/adamyeats/.nvm/v0.10.5/lib/node_modules/local-tld/bin/local-tld-service</string>
        </array>
        <key>KeepAlive</key>
        <true/>
        <key>RunAtLoad</key>
        <true/>
</dict>
</plist>
```

Updating it to this fixed the issue:

```
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Label</key>
        <string>ie.hood.local-tld-service</string>
        <key>ProgramArguments</key>
        <array>
                <string>/Users/adamyeats/.nvm/v0.10.5/bin/node</string>
                <string>/Users/adamyeats/.nvm/v0.10.5/lib/node_modules/local-tld/bin/local-tld-service</string>
        </array>
        <key>KeepAlive</key>
        <true/>
        <key>RunAtLoad</key>
        <true/>
</dict>
</plist>
```

This pull request is intended to make the language of the troubleshooting section a little clearer, and to give an explicit mention to the fact that custom Node installations appear not to be supported by `local-tld` yet. Please get back to me if there are any changes you'd like me to make.