Mark manifest.[go|js] as a generated file (#57)

manifest.[go|js] files are autogenerated so we dont need to
show diffs, cope with conflicts in merge operations or show the
diff in github.

.gitattributes

@@ -0,0 +1,2 @@
+server/manifest.go linguist-generated=true
+webapp/src/manifest.js linguist-generated=true

build/manifest/main.go

@@ -10,7 +10,9 @@ import (
 	"github.com/pkg/errors"
 )
 
-const pluginIDGoFileTemplate = `package main
+const pluginIDGoFileTemplate = `// This file is automatically generated. Do not modify it manually.
+
+package main
 
 var manifest = struct {
 	ID      string
@@ -21,7 +23,9 @@ var manifest = struct {
 }
 `
 
-const pluginIDJSFileTemplate = `export const id = '%s';
+const pluginIDJSFileTemplate = `// This file is automatically generated. Do not modify it manually.
+
+export const id = '%s';
 export const version = '%s';
 `
 

server/manifest.go

@@ -1,3 +1,5 @@
+// This file is automatically generated. Do not modify it manually.
+
 package main
 
 var manifest = struct {

webapp/src/manifest.js

@@ -1,2 +1,4 @@
+// This file is automatically generated. Do not modify it manually.
+
 export const id = 'com.mattermost.plugin-starter-template';
 export const version = '0.1.0';