Update CVE ID Search Field Text

[jfhiggins]

Improve readability in the search field by changing the example text to:

Enter CVE ID (format: CVE-YYYY-NNNN)

[jfhiggins]

@athu-tran @rroberge

Suggestions per discussion:

• change text to "Need a CVE Record? Find one by keyword on cve.mitre.org"
• move text to either left of or underneath the search box

[jfhiggins]

per @rroberge: shorten text further to:

"Find CVE Records by keyword on cve.mitre.org"

[jfhiggins]

Updated mockup for demo/presentation: