docs: add `srcDir` to app config (#1430)

Co-authored-by: Divyansh Singh <40380293+brc-dd@users.noreply.github.com>

docs/config/app-configs.md

@@ -194,6 +194,19 @@ export default {
 }
 ```
 
+## srcDir
+
+- Type: `string`
+- Default: `.`
+
+The directory where your markdown pages are stored, relative to project root. 
+
+```ts
+export default {
+  srcDir: './src'
+}
+```
+
 ## title
 
 - Type: `string`