small grammar fix in testscript README (#533)

## Summary

## How was it tested?

Author: savil

testscripts/README.md

@@ -7,12 +7,12 @@ For details on how to write these types of files see:
 + https://bitfieldconsulting.com/golang/test-scripts
 + https://pkg.go.dev/github.com/rogpeppe/go-internal/testscript
 
-In addition to the standard testscript commands, we've also support running devbox
+In addition to the standard testscript commands, we also support running devbox
 commands. Examples include:
 + `devbox init`
 + `devbox add <pkg>`
 + ...
 
 We've also added some handy comparison functions
 + `path.len <number>`: verifies that the PATH environment variable has the given number of entries
-+ `json.superset <superset.json> <subset.json>`: verifies that `superset.json` has all the keys and values present in `subset.json`
++ `json.superset <superset.json> <subset.json>`: verifies that `superset.json` has all the keys and values present in `subset.json`