feat(perf): Add Python Snippet for Custom Perf Metrics

src/includes/performance/custom-performance-metrics/python.mdx

@@ -0,0 +1,25 @@
+Adding custom metrics is supported in Sentry's Python SDK version `1.5.12` and above.
+
+To enable the capturing of custom metrics, you'll need to enable the `custom_measurements` experiment option.
+
+```python
+sentry_sdk.init(
+    dsn="__DSN__",
+    _experiments={
+        "custom_measurements": True,
+    },
+)
+```
+
+```python
+transaction = Hub.current.scope.transaction;
+
+# Record amount of memory used
+transaction.set_measurement('memory_used', 123, 'byte');
+
+# Record time when job was started
+transaction.set_measurement('job_start_time', 1.3, 'second');
+
+# Record amount of times cache was read
+transaction.set_measurement('cache_read_count', 4);
+```

src/platforms/common/performance/instrumentation/performance-metrics.mdx

@@ -3,12 +3,12 @@ title: Performance Metrics
 sidebar_order: 20
 supported:
   - javascript
+  - python
 notSupported:
   - javascript.cordova
   - javascript.electron
   - react-native
   - dotnet
-  - python
   - go
   - java
   - android