Ability to customize help display behaviour of script name & description via `bashly-strings.yml`#619

### Description When executing the `--help` flag directly on the root script, bashly prints a `<root-name>[ - <root-help>]` string that identifies the script's global name/purpose on the first line of the output. Generally, that makes sense, but I'd like to suppress or customise it in my use case. I have a hip, colourful ASCII art preamble that I am currently outputting on _all_ script executions via `initialize.sh`, which I don't care to report how long I spent crafting whilst procrastinating over my core task 😄. This presents a couple of minor problems: 1. There is a level of duplication when executing `<script> --help` in that the `<root-name>[ - <root-help>]` preamble string is extraneous in my case since that info (and more) is in my custom header. 2. Whilst I am impressed by my own glorious terminal artwork, I have a feeling I will, in the end, only want it to be displayed on `<script> --help` and not on every execution in order to recognise the reality of the unappreciative user's sanity :P. Both problems could probably be solved if this string was customisable in `bashly-strings.yml`. If I only cared about (1) and was happy to keep my preamble on all commands, I could then just null out the hypothetical string template for this in that configuration. If I wanted (2), then I could interpolate some bash into that same string template instead to have my own custom preamble defined there such that it only shows on `<script> --help` . Worth noting for anyone googling that it doesn't make sense to change/null this out in the `bashly.yaml` root `name` field since that is used for various other operational things and so it's scope is beyond just "display". An aside: I used this lib some years ago for a whole trough of internal tooling, and it's awesome to see some little challenges I encountered back then have been addressed as I revisit sometime later in an open-source context. Your dedication to this (incredibly time-saving) project that I've noticed whilst lurking on various GitHub threads is admirable! May I suggest a "built with bashly" community-contributed discussion thread/docs page or something?