Update website build instructions

Author: Kobzol

site/README.md

@@ -7,13 +7,28 @@ which displays graphs to the user.
 This also contains a GitHub bot to trigger on-demand benchmarking.
 
 ## Setup
-
-The site launches on port 2346 by default, which can be overridden by setting
-the `PORT` environment variable.
-
-```
-git clone https://github.com/rust-lang/rustc-perf.git
-```
+You can build the website in multiple ways:
+- Download a precompiled [nightly build](https://github.com/rust-lang/rustc-perf/releases).
+- Use the provided Docker image:
+  ```console
+  $ git clone https://github.com/rust-lang/rustc-perf.git
+  $ docker build -t rustc-perf .
+  ```
+- Build it yourself:
+  ```console
+  $ git clone https://github.com/rust-lang/rustc-perf.git
+  
+  # Build frontend
+  $ cd site/frontend
+  $ npm run build
+  
+  # Build website binary
+  $ cd ../..
+  $ cargo build --bin site --release
+  ```
+  The `--release` flag is on purpose, reducing startup time 15x from roughly 15
+  seconds to 1; this is on the production database and smaller data sets are
+  likely to load considerably faster.
 
 ## Launching
 
@@ -22,10 +37,9 @@ local database. By default, a database called results.db located at the root of
 the project will be used. You can optionally pass a path to a database
 if you don't want to use the default.
 
-```
-cargo run --bin site --release <database>
-```
+The site launches on port 2346 by default, which can be overridden by setting
+the `PORT` environment variable.
 
-The `--release` flag is on purpose, reducing startup time 15x from roughly 15
-seconds to 1; this is on the production database and smaller data sets are
-likely to load considerably faster.
+```console
+$ ./target/release/site <database>
+```