Add pkg-config to required Linux dependencies
Without it, cargo started erroring out for me after saying it
couldn't find openssl without pkg-config being installed.
@@ -153,10 +153,10 @@ On most distributions, you'll need to build from source using `cargo` directly.
#### Build using `cargo`
-First make sure that you have the `libssl-dev` and `openssl` packages installed
-by running something like this:
+First make sure that you have the `libssl-dev`, `openssl`, and `pkg-config`
+packages installed by running something like this:
```shell script
-sudo apt-get install libssl-dev openssl
+sudo apt-get install libssl-dev openssl pkg-config
```
Now run:
