Update usage.md
For compilation of electrs to work in Ubuntu 20.04 build-essential package needs to be installed.
@@ -11,7 +11,7 @@ and [latest Electrum wallet](https://electrum.org/#download) (3.3+).
Also, install the following packages (on Debian):
```bash
$ sudo apt update
-$ sudo apt install clang cmake # for building 'rust-rocksdb'
+$ sudo apt install clang cmake build-essential # for building 'rust-rocksdb'
```
Note for Raspberry Pi 4 owners: the old versions of OS/toolchains produce broken binaries. Make sure to use latest OS! (see #226)
