Minor issues and documentation around tarballed modules

IPM already supports `zpm "load app.tgz"` for convenient loading of packages distributed more manually, but this is not obvious from the wiki documentation. The wiki [mentions](https://github.com/intersystems/ipm/wiki/02.-CLI-commands#load) an example of `load` for a `.tgz` file, but the note right underneath seems out of place.

When trying this, I found that the presence of `.git` metadata folders in the tarball also causes errors:
```
AIDX>zpm "load C:\tmp\app.tgz"
ERROR! Unable to copy file 'C:\InterSystems\I4H\mgr\Temp\XGymDpr2.stream' to 'C:\InterSystems\I4H\mgr\Temp\FnOtH31w\PaxHeader\.git'
```
excluding those folders made it load fine, however, after successful unpacking and loading of a tarballed module, it seems the extracted contents lingers under `IRISHOME/mgr/Temp/`, when in fact it should be removed.

Suggestions:
* adapt the `load` documentation to make it more clear that / how loading from tarballs is supported
* include documentation on how to create such tarballs, noting that git metadata should be excluded, e.g. using a command like this:
```Shell
tar czf app.tgz --exclude .git .
```
* ensure extracted data gets cleaned up, or at the very least output a warning this is up to the user