Adding examples (#8500)

Adding examples to 3 tables!

schema/tables/etc_services.yml

@@ -0,0 +1,10 @@
+name: etc_services
+examples: >-
+  Identify the TCP and UDP ports associated to standard services.
+
+  ```
+
+  SELECT * FROM etc_services WHERE name='ftp';
+
+  ```
+

schema/tables/power_sensors.yml

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+name: power_sensors
+notes: Returns useful results on Intel Macs only.
+examples: >-
+  See the total power usage of an Intel Mac.
+  
+  ```
+  
+  SELECT * FROM power_sensors WHERE key='PSTR';
+  
+  ```

schema/tables/yara.yml

@@ -0,0 +1,16 @@
+name: yara
+examples: >-
+  Look for files under `/root` that match a Yara signature. This example uses the [EICAR test file](https://www.eicar.org/download-anti-malware-testfile/).
+
+  ```
+
+  SELECT * FROM yara WHERE path like '/root/%%' AND sigrule IN (
+    'rule eicar {
+    strings:
+    $s1 = "X5O!P%@AP[4\\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*" fullword ascii
+    condition:
+    all of them
+  }'
+   ) AND matches='eicar';
+
+  ```