Update README

tonic/README

@@ -8,36 +8,42 @@ of various parameters.
 
 Here is an example input object.
 
+```go
     type MyInput struct {
         Foo int    `path:"foo"`
         Bar string `query:"bar" default:"foobar"`
         Baz string `json:"baz"`
     }
+```
 
 Output objects can be of any type, and will be marshaled to JSON.
 
 Input validation is performed after binding into the object using the validator library
 (https://github.com/go-playground/validator). You can use the tag 'validate' on your object
 definition to perform validation inside the tonic handler phase.
 
+```go
     type MyInput struct {
         Foo int    `path:"foo" validate:"required,gt=10"`
         Bar string `query:"bar" default:"foobar" validate:"nefield=Baz"`
         Baz string `json:"baz" validate:"required,email"`
     }
+```
 
 enum input validation is also implemented natively by tonic, and can check that the provided input
 value corresponds to one of the expected enum values.
 
+```go
     type MyInput struct {
         Bar string `query:"bar" enum:"foo,buz,biz"`
     }
-
+```
 
 The handler can return an error, which will be returned to the caller.
 
 Here is a basic application that greets a user on http://localhost:8080/hello/me
 
+```go
     import (
          "errors"
          "fmt"
@@ -66,7 +72,7 @@ Here is a basic application that greets a user on http://localhost:8080/hello/me
         r.GET("/hello/:name", tonic.Handler(GreetUser, 200))
         r.Run(":8080")
     }
-
+```
 
 If needed, you can also override different parts of the logic via certain available hooks in tonic:
     - binding
@@ -82,6 +88,7 @@ We provide a ready-to-use error hook that depends on the juju/errors package (ri
 
 Example of the same application as before, using juju errors:
 
+```go
     import (
          "fmt"
 
@@ -112,6 +119,6 @@ Example of the same application as before, using juju errors:
         r.GET("/hello/:name", tonic.Handler(GreetUser, 200))
         r.Run(":8080")
     }
-
+```
 
 You can also easily serve auto-generated swagger documentation (using tonic data) with https://github.com/wi2l/fizz