goal documentation - clarify when arguments should specify a file

## Summary
Looking at the CLI help it isn't always clear what arguments should reference a file. In many cases we accept base64 encoded strings.

For example `goal clerk send` has two arguments which I think are files, but could just as easily be base64 encoded strings. These fields should say that they expect a file:
```
-F, --from-program string Program source to use as account logic
-P, --from-program-bytes string Program binary to use as account logic
```
## Scope/Requirements
Go through the CLI documentation and update descriptions to clarify whether an argument should point to a file.

## Urgency/Relative Priority
Internal issue, but an easy fix that would improve usability.