docs: Copy-edit headings a bit (react-bootstrap#5191)

Author: taion

www/src/components/SideNav.js

@@ -172,7 +172,10 @@ function NavSection({ heading, location: { pathname }, items, path }) {
           {items.map((name) => (
             <Nav.Item key={`${path}/${name}/`}>
               <TocSubLink href={`${path}/${name}/`}>
-                {startCase(name.toLowerCase())}
+                {startCase(name.toLowerCase()).replace(
+                  'React Bootstrap',
+                  'React-Bootstrap',
+                )}
               </TocSubLink>
             </Nav.Item>
           ))}

www/src/pages/components/forms.js

@@ -245,7 +245,7 @@ export default withLayout(function FormControlsSection({ data }) {
       <ReactPlayground codeText={ValidationNative} />
 
       <LinkedHeading h="3" id="forms-validation-libraries">
-        Form libraries and server rendered styles.
+        Form libraries and server-rendered styles
       </LinkedHeading>
       <p>
         It's often beneficial (especially in React) to handle form validation

www/src/pages/getting-started/theming.js

@@ -11,7 +11,7 @@ export default withLayout(function ThemingSection() {
   return (
     <>
       <LinkedHeading h="1" id="custom-styles">
-        Theming and Customizing styles.
+        Theming and customizing styles
       </LinkedHeading>
 
       <p>

www/src/pages/getting-started/why-react-bootstrap.mdx

@@ -1,7 +1,7 @@
 import DismissibleControlled from '../../examples/Alert/DismissibleControlled';
 import ReactPlayground from '../../components/ReactPlayground';
 
-# Why React-bootstrap?
+# Why React-Bootstrap?
 React-Bootstrap is a complete re-implementation of the
 Bootstrap components using React. It has **no dependency
 on either `bootstrap.js` or jQuery.** If you have React