Rename psalm.phar to psalm

[thePanz]

When using this package the executable phar is called vendor/bin/psalm.phar
This could lead to some confusion when the official guide is used, as it refers to vendor/bin/psalm as the command to run.

[bdsl]

@thePanz I hadn't seen your issue but I just made PR vimeo/psalm#1748 in the main repo to fix exactly this issue. It doesn't rename psalm.phar since there may now be build pipelines that require it to have that name, but it adds an executable PHP file called psalm which requires psalm.phar.

[thePanz]

Great! Thanks

[bdsl]

@muglug has merged the PR, so this should be fixed in the next release.