CONTRIBUTE.md: Fix grammatical errors

Fix grammatical errors making the document read better. Also fixes
a typo.

Closes #3525
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>

docs/CONTRIBUTE.md

@@ -20,8 +20,8 @@ Before posting to one of the curl mailing lists, please read up on the
 We also hang out on IRC in #curl on irc.freenode.net
 
 If you're at all interested in the code side of things, consider clicking
-'watch' on the [curl repo on github](https://github.com/curl/curl) to get
-notified on pull requests and new issues posted there.
+'watch' on the [curl repo on github](https://github.com/curl/curl) to be
+notified of pull requests and new issues posted there.
 
 ### License and copyright
 
@@ -155,7 +155,7 @@ to loose in the flood of many emails, like they sometimes do on the mailing
 lists.
 
 Every pull request submitted will automatically be tested in several different
-ways. Every pull request is verfied that:
+ways. Every pull request is verified for each of the following:
 
  - ... it still builds, warning-free, on Linux and macOS, with both
    clang and gcc