Merge pull request #299 from SmartContractSecurity/chaals-patch-4

Update SWC-101.md

entries/docs/SWC-101.md

@@ -1,3 +1,14 @@
+# Please note, this content is no longer actively maintained.
+
+The content of the SWC registry has not been thoroughly updated since 2020. It is known to be incomplete and may contain errors as well as crucial omissions.
+
+For currently maintained guidance on known Smart Contract vulnerabilities written primarily as guidance for security reviewers, please see the
+[EEA EthTrust Security Levels specification](https://entethalliance.org/specs/ethtrust-sl). As well as the latest release version, an
+[Editor's draft](https://entethalliance.github.io/eta-registry/security-levels-spec.html) is available, that represents the latest work of the group developing the specification.
+
+General guidance for developers on what to consider to ensure security, that is currently maintained, is also available through the 
+[Smart Contract Security Verification Standard (SCSVS)](https://github.com/ComposableSecurity/SCSVS).
+
 # Title
 
 Integer Overflow and Underflow
@@ -20,6 +31,12 @@ It is recommended to use vetted safe math libraries for arithmetic operations co
 
 ## Samples
 
+### EEA EthTrust Security Levels Specification
+
+- [**[S] No Overflow/Underflow**](https://entethalliance.org/specs/ethtrust-sl/#req-1-overflow-underflow)
+- [**[M] Safe Overflow/Underflow**](https://entethalliance.org/specs/ethtrust-sl/#req-2-overflow-underflow)
+- [**[M] Document Special Code Use**](https://entethalliance.org/specs/ethtrust-sl/#req-2-documented)
+
 ### tokensalechallenge.sol
 
 ```solidity