nix log: Add examples

src/nix/log.cc

@@ -19,7 +19,25 @@ struct CmdLog : InstallableCommand
 
     std::string description() override
     {
-        return "show the build log of the specified packages or paths";
+        return "show the build log of the specified packages or paths, if available";
+    }
+
+    Examples examples() override
+    {
+        return {
+            Example{
+                "To get the build log of GNU Hello:",
+                "nix log nixpkgs.hello"
+            },
+            Example{
+                "To get the build log of a specific path:",
+                "nix log /nix/store/lmngj4wcm9rkv3w4dfhzhcyij3195hiq-thunderbird-52.2.1"
+            },
+            Example{
+                "To get a build log from a specific binary cache:",
+                "nix log --store https://cache.nixos.org nixpkgs.hello"
+            },
+        };
     }
 
     void run(ref<Store> store) override