Document Post.update() and add it to README

README.md

@@ -22,7 +22,7 @@ const cohost = require("cohost");
   let [project] = await user.getProjects();
 
   // Create Post
-  await cohost.Post.create(project, {
+  let myPostID = await cohost.Post.create(project, {
     postState: 1,
     headline: "hello world from cohost.js",
     adultContent: false,
@@ -31,6 +31,16 @@ const cohost = require("cohost");
     tags: []
   });
 
+  // Edit Post
+  await cohost.Post.update(project, myPostID, {
+    postState: 1,
+    headline: "Hello world from cohost.js!",
+    adultContent: false,
+    blocks: [],
+    cws: [],
+    tags: ["cohost.js"]
+  });
+
   // Get Posts of Project
   let posts = await project.getPosts();
 
@@ -64,10 +74,10 @@ Works:
 - Logging in
 - Getting the posts of a project
 - Creating a post
+- Editing a post
 
 Doesn't work:
 
-- Editing a post: possible, haven't done it
 - Sharing a post: possible, haven't done it
 - Liking a post: possible, haven't done it
 - Getting notifications: possible, haven't done it

lib.js

@@ -265,7 +265,12 @@ class Post {
     return postId;
   }
 
-  /** see {@link create} */
+  /**
+   *
+   * @param {Project} project Project to post to
+   * @param {string} postId ID of the post to update
+   * @param {PostCreate} data
+   */
   static async update(project, postId, data) {
     await fetch(
       "PUT",