Allow for make-readme.sh to be copy/pastable

[Metaxal]

• outsource quickscript-extra-specific sections to other files, with load conditioned on existence of the file.
• if a script-help-string cannot be found, raise a clear error message

[Metaxal]

cc @spdegabrielle if you have more comments or issues

[Metaxal]

Maybe include the #:help-string of each script function also in the readme (@spdegabrielle 's idea)

[Metaxal]

Maybe also menu item, path, key shortcut in a readable way

[script-help-string description]

• Scripts|my-path|my-function (c:s:x): Description of my-function
• Scripts|my-path|my-function2 (c:s:x2): Description of my-function2

Also find a way to not rely on the make-readme.sh shell script, so as to be portable.

[Metaxal]

The name of the package should be a define at the top, so it can be changed everywhere at once.

From @DexterLagan

You could add the license section automatically too
say https://github.com/[user]/[repo]/blob/master/LICENSE