Update Getting Started

[cperezcapote]

Solving https://gitcoin.co/issue/Bounties-Network/bounties.network/13/1457

• I tried to stick to the given design.
• I wasn't sure if I had to add all the sections in https://bounties.network/gettingStarted.html, but I can do it easily anyway.
• The design is responsive, but I can change it if you prefer another behaviour.
• I changed the way files are copy on dist folder, but since I'm not sure if this is going to be a SPA or not I can undo it too.
• I'm not sure about the fonts, I used the same as in index.html but I think they don't match with the given design.

[mbeylin]

addresses #13