We currently don't have any placeholder text in the search input box on media search.

Something like "Search for images, audio, video and more" could be useful.

Acceptance Criteria:

• If the user hasn't inputted a search term, the search input box should have placeholder text that reads "Search for images, audio, video and more"
• If the user removes their search term, the search input box should also show the same placeholder text

During development, please test the following:

• Test this feature while logged in AND logged out
• Test this feature on at least one mobile browser