Set up hot module reloading

[haydenrou]

• Updates the README
• Adds a Makefile to simplify running local development
• Enables hot module reloading (or more specifically just adds a make command to run it)

Options for hot module reloading suggested by Templ are as follows:

1. Built-in support using the committed command. It seems slightly slower than Air but allows for page reloads on save through a proxy. *
2. air - I liked this but it doesn't offer the proxy, perhaps that's not a dealbreaker?
3. wgo - same, but far less popular / used.

• The reload on save doesn't seem to currently work for me, potentially due to the following error: Proxy to target error: http: proxy error: max retries reached. I've mentioned this in the following issue, and the current workaround is just manually reloading for changes to templ files. Changes to Go files seem to require a restart at the moment. Panic on proxy argument when running generate --watch a-h/templ#381 (comment)

Another option is https://github.com/jdudmesh/gomon but I'd rather go with one of the above as they seem a bit more popular.

If the proxy is temperamental or not a blocker then I'm tempted to use air instead as it seems a little nicer from a configuration perspective, but I think we could follow up with this.

Closes #1

[haydenrou]

@jonnyjones99 @codemonium are you opposed to me pushing this up as is to get the updated readme and makefile up?

I am thinking about creating a low priority bug issue which we can look more into the issue described in the PR description, however I don't think it's a blocker for getting something as simple as this out.