Handle updating a post

If a post has been updated, display the date it was updated, along with
the date it was originally published. Hugo automtically updates the
lastmod value in the sitemap, so we don't have to worry about that.

For crawlers, add HTML time tags, along with "datePublished" and
"dateModified" microdata attributes. Currently, Google isn't displaying
the dates of the posts in the search results. Maybe these changes will
fix that.

README.md

@@ -46,7 +46,7 @@ Many of these were easy to add because of Hugo.
 * [mini blog of issues I've run into while programming](https://www.dannyguo.com/friction/)
 * [referral links](https://wwww.dannyguo.com/referrals/)
 
-## Publishing Checklist
+## Checklist for Publishing a Post
 
 1. Upload any images to the dedicated [Imgur album](https://imgur.com/a/mA7JRWp)
 2. Publish the post by removing the `draft` flag
@@ -67,6 +67,17 @@ Many of these were easy to add because of Hugo.
     * [Reddit](https://www.reddit.com/)
     * [Twitter](https://twitter.com/)
 
+## Checklist for Updating a Post
+
+Only do this for substantial changes, not small ones like fixing typos or links.
+
+1. Add the `lastmod` variable to the post's [front
+   matter](https://gohugo.io/content-management/front-matter/#front-matter-variables)
+2. Update the post content
+3. Publish it
+4. If applicable, update the Medium post and/or the dev.to post
+    * Make sure to check embedded content, like code examples
+
 ## License
 
 The content of this project (in the `content` directory) is licensed under the

layouts/blog/single.html

@@ -3,10 +3,13 @@
 {{ end }}
 
 {{ define "main" }}
-    <h1>{{ .Title }}</h1>
-    <div class="subheader">{{.Date.Format "January 2, 2006"}}&nbsp;&nbsp;·&nbsp;&nbsp;{{ .WordCount | lang.NumFmt 0 }} words&nbsp;&nbsp;·&nbsp;&nbsp;~{{ .ReadingTime | lang.NumFmt 0 }} minute{{ if not (eq .ReadingTime 1) }}s{{ end }} to read</div>
+    <article>
+        <h1>{{ .Title }}</h1>
 
-    {{ partial "anchor.html" .Content }}
+        <div class="subheader">{{ if ne .Date .Lastmod }}Updated on <time itemprop="dateModified" datetime="{{ .Lastmod.Format "2006-01-02" }}">{{ .Lastmod.Format "January 2, 2006" }}</time>&nbsp;&nbsp;·&nbsp;&nbsp;Published on {{ end }}<time itemprop="datePublished" datetime="{{ .Date.Format "2006-01-02" }}">{{.Date.Format "January 2, 2006"}}</time>{{ if eq .Date .Lastmod }}&nbsp;&nbsp;·&nbsp;&nbsp;{{ else }}<br>{{ end }}{{ .WordCount | lang.NumFmt 0 }} words&nbsp;&nbsp;·&nbsp;&nbsp;~{{ .ReadingTime | lang.NumFmt 0 }} minute{{ if not (eq .ReadingTime 1) }}s{{ end }} to read</div>
+
+        {{ partial "anchor.html" .Content }}
+    </article>
 
     <hr class="separator">