CWE-390 was missing in main readme.md

updated as part of ossf#531

Signed-off-by: Helge Wehder <[email protected]>

docs/Secure-Coding-Guide-for-Python/readme.md

@@ -70,6 +70,7 @@ It is **not production code** and requires code-style or python best practices t
 |[CWE-703: Improper Check or Handling of Exceptional Conditions](https://cwe.mitre.org/data/definitions/703.html)|Prominent CVE|
 |:----------------------------------------------------------------|:----|
 |[CWE-230: Improper Handling of Missing Values](CWE-703/CWE-230/.)||
+|[CWE-390: Detection of Error Condition without Action](CWE-703/CWE-390/)||
 |[CWE-392: Missing Report of Error Condition](CWE-703/CWE-392/README.md)||
 |[CWE-754: Improper Check for Unusual or Exceptional Conditions](CWE-703/CWE-754/.)||