Document how to run and update to latest theme version.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Author: troglobit

README.md

@@ -1,13 +1,17 @@
 ## Checkout
 
-    cd path/to/your/repos
-    git clone git@github.com:kernelkit/kernelkit.github.io.git blog
-    cd blog/
-    git submodule update --init
+```bash
+cd path/to/your/repos
+git clone git@github.com:kernelkit/kernelkit.github.io.git blog
+cd blog/
+git submodule update --init
+```
 
 Make changes/additions on a separate branch:
 
-    git checkout -b my-changes
+```bash
+git checkout -b my-changes
+```
 
 When you push it to GitHub you will get a question by GitHub.com if you
 want to create a pull request.  Do that and follow the instructions.
@@ -21,6 +25,46 @@ Verified to work on Linux Mint 21.3, based on Ubuntu 22.04 LTS:
  - [Install Jekyll](https://jekyllrb.com/docs/installation/)
  - Run `bundle` from the blog directory to install all deps
 
+
+## Running
+
+With everyting installed, starting the previewer is as simple as:
+
+```bash
+$ jekyll serve
+Configuration file: /home/jocke/src/kernelkit.github.io/_config.yml
+            Source: /home/jocke/src/kernelkit.github.io
+       Destination: /home/jocke/src/kernelkit.github.io/_site
+ Incremental build: disabled. Enable with --incremental
+      Generating... 
+                    done in 0.801 seconds.
+ Auto-regeneration: enabled for '/home/jocke/src/kernelkit.github.io'
+    Server address: http://127.0.0.1:4000/
+  Server running... press ctrl-c to stop.
+```
+
+## Updating
+
+Occasionally we update the Chirpy theme or its dependencies.  To be able
+to continue using the previewer, you need to update your deps:
+
+```bash
+$ bundle update
+Fetching gem metadata from https://rubygems.org/...........
+Resolving dependencies...
+Fetching concurrent-ruby 1.3.4 (was 1.3.3)
+Fetching google-protobuf 4.27.4 (x86_64-linux) (was 4.27.2)
+Fetching rexml 3.3.6 (was 3.3.2)
+Fetching parallel 1.26.3 (was 1.25.1)
+Installing concurrent-ruby 1.3.4 (was 1.3.3)
+Installing google-protobuf 4.27.4 (x86_64-linux) (was 4.27.2)
+Installing rexml 3.3.6 (was 3.3.2)
+Fetching jekyll-theme-chirpy 7.1.0 (was 7.0.1)
+Installing parallel 1.26.3 (was 1.25.1)
+Installing jekyll-theme-chirpy 7.1.0 (was 7.0.1)
+Bundle updated!
+```
+
 ## Identity
 
 All blog posts have one or more authors.  Make sure your nick is added