add purchase link

docs/en/unit/pdm.md

@@ -122,11 +122,9 @@
 
 Please click [here](https://github.com/m5stack/M5-ProductExampleCodes/tree/master/Unit/PDM) to download Arduino Code.
 
-<img src="assets/img/product_pics/unit/unit_example/ADC/example_unit_adc_01.webp">
-
 <script>
 
-   var purchase_link = '';
+   var purchase_link = 'https://m5stack.com/collections/m5-unit/products/pdm-microphone-unit-spm1423';
 
    anchor_search(purchase_link);
    scrollFunc();

docs/en/unit/tvoc.md

@@ -129,7 +129,7 @@ The code below is incomplete. To get the complete code, please click [here](http
 
 <script>
 
-   var purchase_link = '';
+   var purchase_link = 'https://m5stack.com/collections/m5-unit/products/tvoc-eco2-gas-unit-sgp30';
 
    anchor_search(purchase_link);
    scrollFunc();

docs/zh_CN/unit/pdm.md

@@ -103,7 +103,7 @@
         <a>
             <svg id="play-btn" t="1583228776634" class="icon" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="4152" width="75" height="75"><path d="M512 0C229.216 0 0 229.216 0 512s229.216 512 512 512 512-229.216 512-512S794.784 0 512 0z m0 928C282.24 928 96 741.76 96 512S282.24 96 512 96s416 186.24 416 416-186.24 416-416 416zM384 288l384 224-384 224z" p-id="4153" fill="#007aff"></path></svg></a>
             <p>案例描述:</p>
-            <p>PDM Unit接入PORT A(此序不支持M5GO 底座) ，屏幕显示声音频谱</p>
+            <p>PDM Unit接入PORT A(此程序不支持M5GO 底座) ，屏幕显示声音频谱</p>
         </div>
     </div>
 </div>
@@ -121,7 +121,7 @@
 
 <script>
 
-   var purchase_link = '';
+   var purchase_link = 'https://m5stack.com/collections/m5-unit/products/pdm-microphone-unit-spm1423';
 
    anchor_search(purchase_link);
    scrollFunc();

docs/zh_CN/unit/tvoc.md

@@ -130,7 +130,7 @@
 
 <script>
 
-   var purchase_link = '';
+   var purchase_link = 'https://m5stack.com/collections/m5-unit/products/tvoc-eco2-gas-unit-sgp30';
 
    anchor_search(purchase_link);
    scrollFunc();