Add default placeholder for post UI :)

Closes: #18
Changlog-Added: Added post placeholder text (thanks jcarucci27)
Signed-off-by: William Casarin <jb55@jb55.com>

damus/Views/PostView.swift

@@ -12,8 +12,12 @@ enum NostrPostResult {
     case cancel
 }
 
+let POST_PLACEHOLDER = "Type your post here..."
+
 struct PostView: View {
-    @State var post: String = ""
+    @State var post: String = POST_PLACEHOLDER
+    @State var new: Bool = true
+
     @FocusState var focus: Bool
     let references: [ReferencedId]
 
@@ -60,8 +64,17 @@ struct PostView: View {
             }
             .padding([.top, .bottom], 4)
 
+
             TextEditor(text: $post)
+                .foregroundColor(self.post == POST_PLACEHOLDER ? .gray : .primary)
                 .focused($focus)
+                .onTapGesture {
+                    handle_post_placeholder()
+                }
+                .onChange(of: post) { value in
+                    handle_post_placeholder()
+                }
+
         }
         .onAppear() {
             DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
@@ -70,5 +83,14 @@ struct PostView: View {
         }
         .padding()
     }
+
+    func handle_post_placeholder()  {
+        guard new else {
+            return
+        }
+
+        new = false
+        post = post.replacingOccurrences(of: POST_PLACEHOLDER, with: "")
+    }
 }