add missing alts to make SEO better.

src/components/Bg.tsx

@@ -17,11 +17,12 @@ const StyledBg = styled.img`
 
 interface BgProps {
     url: any
+    alt: string
 }
 
-const Bg: React.SFC<BgProps> = ({url}) => (
+const Bg = ({url, alt}: BgProps) => (
     <div className="row">
-        <StyledBg src={url} aria-hidden="true" />
+        <StyledBg src={url} alt={alt}/>
     </div>
 )
 

src/pages/education.tsx

@@ -52,7 +52,7 @@ const EducationPage: React.SFC<{}> = () => (
             title="We eliminate tedious workflows."
         />
 
-        <Bg url={CollegeStudents} />
+        <Bg url={CollegeStudents} alt="Students going to the college"/>
 
         <PricingTable
             title="Gitpod Education Pricing"

src/pages/recruiting.tsx

@@ -47,7 +47,7 @@ const RecrutingPage: React.SFC<{}> = () => (
             title="We create the most convenient dev environments."
         />
 
-        <Bg url={RecruitingBG} />
+        <Bg url={RecruitingBG} alt="A road on Mountains with trees on either side." />
 
         <PricingTable
             title="Gitpod Recruiting Pricing"

src/pages/vendor.tsx

@@ -47,7 +47,7 @@ const VendorPage: React.SFC<{}> = () => (
             title="We’ll make your developer products shine."
         />
 
-        <Bg url={VendorBG} />
+        <Bg url={VendorBG} alt="A large hall with paintings embeded on it's walls." />
 
         <PricingTable
             title="Gitpod Vendor Pricing"