install: add /usr/local/bin to the PATH if not present

[blues-man]

This fixes installation on Linux distributions like CentOS 7, where the /usr/local/bin directory is not in the PATH by default

[fn-bot]

CLA Bot

Thank you for your submission! It appears that the following authors have not signed our Contributor License Agreement:

• Natale Vinto

Please do so now by visiting http://www.oracle.com/technetwork/community/oca-486395.html

Once complete, let us know in our community Slack and we’ll send you an Fn T-shirt.

We are working on modernizing the CLA process into a digital signature but it isn’t quite ready yet.

Thank you for being a part of the Fn Community!

[fn-bot]

CLA Bot

Thank you for your submission! It appears that the following authors have not signed our Contributor License Agreement:

• Natale Vinto

Please do so now by visiting http://www.oracle.com/technetwork/community/oca-486395.html

Once complete, let us know in our community Slack and we’ll send you an Fn T-shirt.

We are working on modernizing the CLA process into a digital signature but it isn’t quite ready yet.

Thank you for being a part of the Fn Community!

[rdallman]

see: https://github.com/fnproject/fn/issues/1395

[fn-bot]

CLA Bot

All committers have signed the CLA.