Set version to 0.7.7 in readme.md (#76)

Add 0.7.7 and 0.7.6 versions to Changelog

Author: lolgab

readme.md

@@ -161,9 +161,9 @@ To begin using OS-Lib, first add it as a dependency to your project's build:
 
 ```scala
 // SBT
-"com.lihaoyi" %% "os-lib" % "0.7.3"
+"com.lihaoyi" %% "os-lib" % "0.7.7"
 // Mill
-ivy"com.lihaoyi::os-lib:0.7.3"
+ivy"com.lihaoyi::os-lib:0.7.7"
 ```
 
 ## Cookbook
@@ -2093,6 +2093,14 @@ string, int or set representations of the `os.PermSet` via:
 
 ## Changelog
 
+### 0.7.7 - 2021-05-14
+
+- Add support for Scala 3.0.0
+
+### 0.7.6 - 2021-04-28
+
+- Add support for Scala 3.0.0-RC3
+
 ### 0.7.5 - 2021-04-21
 
 - Re-added support for Scala 2.11