Docs: set api_key to env (#2252)

docs/features/custom-categories.mdx

@@ -19,9 +19,12 @@ Here's how to set custom categories:
 
 <CodeGroup>
 ```python Code
+import os
 from mem0 import MemoryClient
 
-client = MemoryClient(api_key="<your_mem0_api_key>")
+os.environ["MEM0_API_KEY"] = "your-api-key"
+
+client = MemoryClient()
 
 # Update custom categories
 new_categories = [
@@ -95,8 +98,11 @@ You can also set custom categories during the `add` API call. This will override
 
 <CodeGroup>
 ```python Code
+import os
 from mem0 import MemoryClient
 
+os.environ["MEM0_API_KEY"] = "your-api-key"
+
 client = MemoryClient(api_key="<your_mem0_api_key>")
 
 custom_categories = [
@@ -148,9 +154,12 @@ Here is the list of **default categories**. If you don't specify any custom cate
 
 <CodeGroup>
 ```python Code
+import os
 from mem0 import MemoryClient
 
-client = MemoryClient(api_key="<your_mem0_api_key>")
+os.environ["MEM0_API_KEY"] = "your-api-key"
+
+client = MemoryClient()
 
 messages = [
     {"role": "user", "content": "Hi, my name is Alice."},

docs/features/selective-memory.mdx

@@ -29,9 +29,12 @@ Users can define specific kinds of memories to store. This feature enhances memo
 Here’s how you can do it:
 
 ```python
+import os
 from mem0 import MemoryClient
 
-m = MemoryClient(api_key="xxx")
+os.environ["MEM0_API_KEY"] = "your-api-key"
+
+m = MemoryClient()
 
 # Define what to include
 includes = "sports related things"