Merge #821

821: Fix typo in README r=asomers a=Aaron1011

Author: bors[bot]

README.md

@@ -33,7 +33,7 @@ pub fn gethostname<'a>(buffer: &'a mut [u8]) -> Result<&'a CStr>;
 nix target support consists of two tiers. While nix attempts to support all
 platforms supported by [libc](https://github.com/rust-lang/libc), only some
 platforms are actively supported due to either technical or manpower
-limitations. Support for platforms is split into two tiers:
+limitations. Support for platforms is split into three tiers:
 
   * Tier 1 - Builds and tests for this target are run in CI. Failures of either
              block the inclusion of new code.