Fix weird sentence constructs in README (#8)

* Fix weird sentence construct in README

* Change singular tense in README

CHANGELOG.md

@@ -2,12 +2,12 @@
 
 ## `v0.2.1`
 
-- Fix exit code not return non-zero value during error
+- Fix and return non-zero exit code during error
   ([#6](https://github.com/guangie88/tera-cli/pull/6)).
 
 ## `v0.2.0`
 
-- Drops root key support entirely
+- Drop root key support entirely
   ([#4](https://github.com/guangie88/tera-cli/pull/4)).
   Only allow variable file to contain `map[string, value]` at root. The keys of
   the map now forms the root keys.
@@ -23,4 +23,4 @@
 ## `v0.1.0`
 
 - Initial implementation with JSON, TOML and env var support.
-- Reads all possible values into a default root key `c`.
+- Read all possible values into a default root key `c`.