Skill installer default branch + shorthand syntax

[DannyBen]

It would be nice if the skill installer does not default to "main" branch, and instead uses the repo's default branch. Just do a git clone without providing a ref unless explicitly requested by the user.

It would also be nice if a discovery of the skill path would be performed.
This can probably be achieved in one of three ways:

1. automated discovery by the AI itself
2. config file (.openai.conf) in the root dir of the repo
3. convention (e.g. "skills/SKILL/SKILL.md")

For example, for the skill I created on master branch, the shortest install instructions I found to work were:

install the skill from https://github.com/bashly-framework/bashly-ai-kit/tree/master/skills/bashly (master branch)

whereas I would love to avoid the "master branch" specification, and the full GitHub URL. Ideally, I would want:

install the bashly skill from github: bashly-framework/bashly-ai-kit
# or
$skill-installer github:bashly-framework/bashly-ai-kit

I know there are flags that can be provided, but using natural language to do these operations seems more appropriate.