doc: fix typos and grammatical errors in contribute.html

Fixed some typos and grammatical errors in contribute.html

Change-Id: Ifb31f22d876b7bea84b5e130870c26813b2fa139
GitHub-Last-Rev: 43519198859ca8f5e1c870b8f3eeb1b465aa6bc5
GitHub-Pull-Request: golang/go#39892
Reviewed-on: https://go-review.googlesource.com/c/go/+/240277
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/doc/contribute.html b/doc/contribute.html
index 6188ee1..03d02c9 100644
--- a/doc/contribute.html
+++ b/doc/contribute.html
@@ -174,7 +174,7 @@
 a Git server hosted by Google.
 Authentication on the web server is made through your Google account, but
 you also need to configure <code>git</code> on your computer to access it.
-Follow this steps:
+Follow these steps:
 </p>
 
 <ol>
@@ -310,7 +310,7 @@
 	<b>NeedsDecision</b>: the issue is relatively well understood, but the
 	Go team hasn't yet decided the best way to address it.
 	It would be better to wait for a decision before writing code.
-	If you are interested on working on an issue in this state,
+	If you are interested in working on an issue in this state,
 	feel free to "ping" maintainers in the issue's comments
 	if some time has passed without a decision.
 	</li>