added usage of r prefix and string interpolation

Signed-off-by: d4v1d03 <a_pandey1@ce.iitr.ac.in>

Author: d4v1d03

docs/user_docs/support/faq-kcl.md

@@ -2492,4 +2492,21 @@ config = {
     age = 25
 }
 alice: Person = config
-```
+```
+
+## 58. Please explain the relationship and usage of 'r' prefix in a String and String Interpolation.
+
+In KCL, we can use `${..}` for string interpolation. But in some cases, we don't want to escape it. Therefore, we use create a raw string by prefixing the string literal with `'r'` or `'R'`. An example KCL code over here is:
+
+```KCL
+worldString = "world"
+s = "Hello ${worldString}"
+raw_s = r"Hello ${worldString}"  
+```
+
+The output comes out as:
+
+```bash
+worldString: world
+s: Hello world
+raw_s: Hello ${worldString}