Adding constants info

docs/templating-guide/variables.md

@@ -67,4 +67,46 @@ tcp:
         part: data
         words:
           - "{{a2}}"
-```
+```
+
+### Constants
+In addition to variables, you can also define constants in templates. Constants are similar to variables but have a distinct difference: their values cannot be overridden or changed, even by command-line variables. They are used to declare scalar values that remain fixed throughout the template. Constants are helpful when you want to ensure that a specific value remains unchanged across multiple template executions.
+
+To declare a constant, use the `constants` keyword followed by the constant name and its value. Constants are declared at the template level, just like variables.
+
+Example constants:
+
+```yaml
+constants:
+  p: test
+```
+
+In the above example, `p` is a constant with the values `test`
+
+Here's an example template that uses constants:
+
+```yaml
+id: constants-example
+
+info:
+  name: Constants Example
+  author: pdteam
+  severity: info
+
+constants:
+  p: test
+
+http:
+  - raw:
+      - |
+        GET /api/data?param={{p}} HTTP/1.1
+        Host: {{Hostname}}
+    matchers:
+      - type: word
+        words: 
+          - "OK"
+```
+
+If the same variable is passed via CLI, the value remains `test` (`nuclei -V p=anothervalue ...`).
+
+Constants provide a way to ensure that specific values remain constant and cannot be modified, providing consistency and predictability in your templates.