Update sponsors.md

Author: Hubertus Tummescheit

content/events/american2024/sponsors.md

@@ -3,18 +3,18 @@
 <table>
     <tr>
         <td>Platinum</td>
-        <td colspan="4" align="center"><img src="modelon.jpg" width="400"></td>
+        <td colspan="4" align="center"><img src="modelon.jpg" width="400" alt="Modelon"></td>
     </tr>
     <tr>
         <td>Gold</td>
-        <td><img src="claytex.jpg" width="250"></td>
+        <td><img src="claytex.jpg" width="250" alt="Claytex"></td>
         <td><img src="3ds2.jpeg" width="250"></td>
-        <td><img src="2020_11_04_MKTG_ESI_Logo_ColorTagline_rgb.png" width="250"></td>
-        <td><img src="juliacomputing.jpg" width="250"></td>
+        <td><img src="2020_11_04_MKTG_ESI_Logo_ColorTagline_rgb.png" width="250" alt="ESI"></td>
+        <td><img src="juliacomputing.jpg" width="250" alt="Julia Computing"></td>
     </tr>
     <tr>
         <td>Silver</td>
-        <td><img src="maplesoft.jpg" width="250"></td>
+        <td><img src="maplesoft.jpg" width="250" alt="Maplesoft"></td>
         <td></td>
         <td></td>
         <td></td>