Some minor restructuring of the SASS files to reflect the architecture of USWDS

Add a brief README explaining best practices for styling
Add comment annotations to the top of each file that references the original USWDS documentation and source

scss/elements/_typography.scss

@@ -0,0 +1,24 @@
+/*
+ * Typography
+ * @see https://designsystem.digital.gov/components/typography/
+ * @source https://github.com/uswds/uswds/blob/develop/src/stylesheets/elements/_typography.scss
+ */
+
+h1, h2, h3, h4, h5, h6 {
+  font-family: $font-sans;
+
+  .usa-button {
+    position: relative;
+    bottom: 0.5rem;
+    left: 1rem;
+  }
+
+}
+
+h1 {
+  margin-top: 0.5em;
+}
+
+h2 {
+  margin-top: 0;
+}