CONTRIBUTING.md: minor changes

- Misspelled GitHub
- angle bracket not escaped correctly
- Double white spaces
- White spaces at EOL

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/788

CONTRIBUTING.md

@@ -41,7 +41,7 @@ A pull request will be considered if:
 * The commits follow FreeBSD's style guide. See [Style](#Style).
 * Run tools/build/checkstyle9.pl on your Git branch and eliminate all errors
 * The commits do not introduce trailing white space.
-* If the commmit fixes a bug, please add 'PR: \<bugnumber>\' to the commit message.
+* If the commmit fixes a bug, please add 'PR: \<bugnumber\>' to the commit message.
 * If there's a code review in Phabricator, please include a link as a 'Differential Revision: ' line.
 
 When updating your pull request, please rebase with a forced push rather than a
@@ -72,7 +72,7 @@ project. The guidelines are streamlined for quick decisions about each pull
 request. Unless explicitly stated, rejection here as "not ready" or "too large"
 does not mean the project is uninterested in the work, it just means the
 submission does not meet the limited scope for pull requests accepted
-here. Sometimes it is easier to review a GihHub pull request than to do the
+here. Sometimes it is easier to review a GitHub pull request than to do the
 review in Phabricator, so that's also allowed.
 
 ## Style