Rename "Installation" tab on plugins details page

[johnbillion]

Migrating this general issue from ​#wp20318, but updating based on the comments here.

We should consider renaming the "Installation" tab on the plugin details page. Per comments in ​#wp20318, using "Installation" is rather confusing because plugins in the directory are all easily installed through WordPress.

Proposed rename is "Instructions", taking its content from either the Instructions section in readme.txt or from the Installation section to preserver back-compat.

(Also discussed was "Usage" or "Directions", but "Instructions" won in the comments.)

We should propose this publicly and see what plugin developers think of it. Perhaps the Plugins team has input here?

[kpdesign]

+1 for Instructions. Makes more sense now that users can install plugins from wp-admin.

[Ipstenu-DH]

+1 for Instructions!

[samuelsidler]

If we do this – I still think we should get some feedback from the plugin team – we need to make sure we update the readme parser as well to look for "Instructions" not just "Installation".

But I support this change.

[samuelsidler]

We're agreed on "Instructions" and making the parser changes to not only look for Instructions, but also merge "Installation" and "Instructions" when they're both present.

[SergeyBiryukov]

We would also need to change it in core:
​https://core.trac.wordpress.org/browser/tags/3.9.1/src/wp-admin/includes/plugin-install.php#L327

[ocean90]

I don't think we should just rename the tab. I think we should introduce a new tab, called "Usage" (or "Instructions"), which contains new content (usage and instructions). The "Installation" tab then gets deprecated.
Idea from @samuelsidler: "If the new tab exists, don’t show Installation. But if it doesn’t exist, show Installation"

[ramiy]

+1 for "Usage".

[samuelsidler]

I'm actually going to close this as wontfix. The new directory in-progress removes installation in favor of... nothing. There are other improvements we can make to give plugin developers a way to show usage/installation information.