feat(tools): Add a horrifying tool to write blog posts into DNS

tools/blog_cli/README.md

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+tazblog CLI
+===========
+
+My blog stores its content in DNS, spread out over three types of `TXT` entries:
+
+* `TXT _posts.blog.tazj.in.`: A sorted list of posts, serialised as a JSON list of
+  strings (e.g. `["1486830338", "1476807384"]`)
+
+* `TXT _chunks.$postID.blog.tazj.in`: JSON chunks containing the blog post text
+
+* `TXT _meta.$postID.blog.tazj.in`: JSON blob with blog post metadata
+
+All JSON blobs are base64-encoded.
+
+This CLI tool helps to update those records.
+
+Each blog post data is a series of JSON-encoded structures which follow one of
+these formats:
+
+```
+struct metadata {
+    chunks: int
+    title: string
+    date: date
+}
+```
+
+Where `chunks` describes the number of chunks following this format:
+
+```
+struct chunk {
+    c: int
+    t: string
+}
+```
+
+Writing a blog post to DNS means taking its text and metadata, chunking it up
+and writing the chunks.
+
+Reading a blog post means retrieving all data, reading the metadata and then
+assembling the chunks in order.