Documentation: Minor corrections of several md files (#1806)

CODE_OF_CONDUCT.md

@@ -293,7 +293,7 @@ violation of this Code of Conduct using these guidelines based on the behavior
 involved:
 
 1.  **Correction**
-    -   **Behavior:** Use of inappropriate language or other minor violations
+    -   **Behavior:** Use of inappropriate language or other minor violations of
         the code of conduct.
     -   **Action:** A private, written message providing clarity around the
         nature of the violation and an explanation of why the behavior was

CONTRIBUTING.md

@@ -182,8 +182,7 @@ follow the Carbon documentation and coding styles.
 
     -   When the Carbon team accepts new documentation or features, to Carbon,
         by default they take on the maintenance burden. This means they'll weigh
-        the benefit of each contribution must be weighed against the cost of
-        maintaining it.
+        the benefit of each contribution against the cost of maintaining it.
     -   The appropriate [style](#style) is applied.
     -   The [license](#license) is present in all contributions.
     -   [Code review](/docs/project/code_review.md) is used to improve the

docs/project/cpp_style_guide.md

@@ -40,7 +40,7 @@ The baseline style guidance is the
 
 ## Carbon-local guidance
 
-We provide some local guidance beyond the baseline. This are typically motived
+We provide some local guidance beyond the baseline. These are typically motived
 either by specific value provided to the project, or to give simpler and more
 strict guidance for Carbon's narrow use of C++.