Add Venmo and Square Cash App icons (#208)

* add Venmo and Square Cash App icons

* proper `aria-label` 😅

images/reference/index.md

@@ -151,3 +151,5 @@ Where possible this links to the organisation's brand guidelines page.
 | <img src="/images/svg/opera.svg" width="256" /> | <img src="/images/reference/opera.png" width="256" />  | https://brand.opera.com/ |
 | <img src="/images/svg/firefox.svg" width="256" /> | <img src="/images/reference/firefox.svg" width="256" />  | https://design.firefox.com/photon/visuals/product-identity-assets.html |
 | <img src="/images/svg/raspberry_pi.svg" width="256" /> | <img src="/images/reference/RPi-Logo-SCREEN.png" width="256" />  | https://www.raspberrypi.org/trademark-rules/ |
+| <img src="/images/svg/venmo.svg" width="256" /> | <img src="/images/reference/venmo-icon.svg" width="256" />  | https://venmo.com/about/brand |
+| <img src="/images/svg/square-cash.svg" width="256" /> | <img src="/images/reference/square-cash-app-logo.jpg" width="256" />  | https://squareup.com/us/en/press |

images/reference/venmo-icon.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 516 516"><defs><style>.a{fill:#3396cd;}.b{fill:#fff;}</style></defs><title>venmo-icon</title><rect class="a" width="516" height="516" rx="61" ry="61"/><path class="b" d="M385.16,105c11.1,18.3,16.08,37.17,16.08,61,0,76-64.87,174.7-117.52,244H163.49L115.28,121.65l105.31-10L246.2,316.82C270,278,299.43,217,299.43,175.44c0-22.77-3.9-38.25-10-51Z"/></svg>