Merge pull request #375 from carlpett/patch-1

docs: Add missing link to url functions

docs/index.md

@@ -22,3 +22,4 @@ The Sprig library provides over 70 template functions for Go's template language
   - [Reflection](reflection.md): `typeOf`, `kindIs`, `typeIsLike`, etc.
   - [Cryptographic and Security Functions](crypto.md): `derivePassword`, `sha256sum`, `genPrivateKey`, etc.
   - [Network](network.md): `getHostByName`
+  - [URL](url.md): `urlParse`, `urlJoin`