README: update docs for building web client

Move into the main "building" section and add the missing `yarn install`
step.

Updates #9312

Signed-off-by: Will Norris <will@tailscale.com>

README.md

@@ -41,6 +41,16 @@ We always require the latest Go release, currently Go 1.21. (While we build
 releases with our [Go fork](https://github.com/tailscale/go/), its use is not
 required.)
 
+To include the embedded web client (accessed via the `tailscale web` command),
+first build the client assets using:
+
+```
+./tool/yarn --cwd client/web install
+./tool/yarn --cwd client/web build
+```
+
+Build the `tailscale` and `tailscaled` binaries:
+
 ```
 go install tailscale.com/cmd/tailscale{,d}
 ```
@@ -57,17 +67,6 @@ If your distro has conventions that preclude the use of
 `build_dist.sh`, please do the equivalent of what it does in your
 distro's way, so that bug reports contain useful version information.
 
-## Building the web client
-
-To include the embedded web client (accessed via the `tailscale web` command),
-you'll need to build the client assets using:
-
-```
-./tool/yarn --cwd client/web build
-```
-
-Do this before building the `tailscale.com/cmd/tailscale` binary.
-
 ## Bugs
 
 Please file any issues about this code or the hosted service on