Make ports help text start with uppercase letter to be consistent with other help texts

[antonkesy]

Sorry for the minor changes only and the spam PR.

I've noticed that help ports starting letter case does not match the other commands. ¯\(ツ)/¯

mininet> help nodes
List all nodes.
mininet> help intfs
List interfaces.
mininet> help links
Report on links
mininet> help ports
display ports and interfaces for each switch

[antonkesy]

Update: Added some punctuation too

[antonkesy]

But there are still some cases where I have no idea what style they should follow:

Line:130 "Local variable bindings for py command"

Line:489: "allow for comments in the cli"