Auto merge of #23175 - servo:CYBAI-patch-1, r=jdm

Add a note to indicate PKG_CONFIG_PATH required

I just got the error messages like #23015 again and then I think the root cause should be about
`PKG_CONFIG_PATH`. After following https://github.com/servo/servo/issues/23015#issuecomment-475050175 said, I can build Servo successfully.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because this just updates README.

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bors-servo 2019-04-07 10:56:35 -04:00 committed by GitHub
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@ -76,6 +76,8 @@ export OPENSSL_LIB_DIR="$(brew --prefix openssl)/lib"
./mach build ...
```
##### Note: Please make sure the required `PKG_CONFIG_PATH` environment variable is set the same as the one provided from `brew info libffi` ([Check this comment for more details](https://github.com/servo/servo/issues/23015#issuecomment-475050175)).
If you've already partially compiled servo but forgot to do this step, run `./mach clean`, set the shell variables, and recompile.
#### On Debian-based Linuxes