Fix missing QLDoc

Author: egregius313

csharp/ql/lib/semmle/code/csharp/security/dataflow/flowsources/Local.qll

@@ -31,18 +31,27 @@ class TextFieldSource extends LocalUserInputSource {
   override string getSourceType() { result = "TextBox text" }
 }
 
+/**
+ * A dataflow source that represents the access of an environment variable.
+ */
 abstract class EnvironmentVariableSource extends LocalFlowSource {
   override string getThreatModel() { result = "environment" }
 
   override string getSourceType() { result = "environment variable" }
 }
 
+/**
+ * A dataflow source that represents the access of a command line argument.
+ */
 abstract class CommandLineArgumentSource extends LocalFlowSource {
   override string getThreatModel() { result = "commandargs" }
 
   override string getSourceType() { result = "command line argument" }
 }
 
+/**
+ * A data flow source that represents the parameters of the `Main` method of a program.
+ */
 private class MainMethodArgumentSource extends CommandLineArgumentSource {
   MainMethodArgumentSource() { this.asParameter() = any(MainMethod mainMethod).getAParameter() }
 }