Add Sponsor's Brochure on the sponsors us page

[kkothari2001]

Quick review of the changes required from the current main branch.

Content changes:

• Should be "Sponsor Us" on the navbar.
• Should be "Sponsor Us" in the hero component
• Subtitle should change to "Help us maintain our legacy of excellence!"
• uncapitalize "Seminars" in para 1
• add a central <hr> , width: 40-60% (see what looks the best) after each type of sponsor, color Sass variable $lightest

cc @amanchhaparia