Update about-github-pages.md (#734)

Lately i'm working on an unofficial Chinese translation of GitHub Pages docs due to the incompletion of the original and currently there is no way to contribute translations to the docs. So,  I hope that's ok to you guys.  

The thing is, I'm seeing that this document is using both `<user>` and `<username>` as subdomain pronouns among the context. It's not a big problem, but in my opnion, this might cause some unnecessary confusion to some users.   

If it was intended to be so, I'd like to know why?  
Thank you!

Co-authored-by: hubwriter <hubwriter@github.com>

content/github/working-with-github-pages/about-github-pages.md

@@ -34,9 +34,9 @@ Organization owners can disable the publication of {% data variables.product.pro
 
 There are three types of {% data variables.product.prodname_pages %} sites: project, user, and organization. Project sites are connected to a specific project hosted on {% data variables.product.product_name %}, such as a JavaScript library or a recipe collection. User and organization sites are connected to a specific {% data variables.product.product_name %} account.
 
-To publish a user site, you must create a repository owned by your user account that's named {% if currentVersion == "free-pro-team@latest" %}`<user>.github.io`{% else %}`<user>.<hostname>`{% endif %}. To publish an organization site, you must create a repository owned by an organization that's named {% if currentVersion == "free-pro-team@latest" %}`<organization>.github.io`{% else %}`<organization>.<hostname>`{% endif %}. {% if currentVersion == "free-pro-team@latest" %}Unless you're using a custom domain, user and organization sites are available at `http(s)://<username>.github.io` or `http(s)://<organization>.github.io`.{% elsif currentVersion == "github-ae@latest" %}User and organization sites are available at `http(s)://pages.<hostname>/<username>` or `http(s)://pages.<hostname>/<organization>`.{% endif %}
+To publish a user site, you must create a repository owned by your user account that's named {% if currentVersion == "free-pro-team@latest" %}`<username>.github.io`{% else %}`<username>.<hostname>`{% endif %}. To publish an organization site, you must create a repository owned by an organization that's named {% if currentVersion == "free-pro-team@latest" %}`<organization>.github.io`{% else %}`<organization>.<hostname>`{% endif %}. {% if currentVersion == "free-pro-team@latest" %}Unless you're using a custom domain, user and organization sites are available at `http(s)://<username>.github.io` or `http(s)://<organization>.github.io`.{% elsif currentVersion == "github-ae@latest" %}User and organization sites are available at `http(s)://pages.<hostname>/<username>` or `http(s)://pages.<hostname>/<organization>`.{% endif %}
 
-The source files for a project site are stored in the same repository as their project. {% if currentVersion == "free-pro-team@latest" %}Unless you're using a custom domain, project sites are available at `http(s)://<user>.github.io/<repository>` or `http(s)://<organization>.github.io/<repository>`.{% elsif currentVersion == "github-ae@latest" %}Project sites are available at `http(s)://pages.<hostname>/<username>/<repository>/` or `http(s)://pages.<hostname>/<organization>/<repository>/`.{% endif %}
+The source files for a project site are stored in the same repository as their project. {% if currentVersion == "free-pro-team@latest" %}Unless you're using a custom domain, project sites are available at `http(s)://<username>.github.io/<repository>` or `http(s)://<organization>.github.io/<repository>`.{% elsif currentVersion == "github-ae@latest" %}Project sites are available at `http(s)://pages.<hostname>/<username>/<repository>/` or `http(s)://pages.<hostname>/<organization>/<repository>/`.{% endif %}
 
 {% if currentVersion == "free-pro-team@latest" %}
 For more information about how custom domains affect the URL for your site, see "[About custom domains and {% data variables.product.prodname_pages %}](/articles/about-custom-domains-and-github-pages)."
@@ -60,7 +60,7 @@ For more information, see "[Enabling subdomain isolation](/enterprise/{{ current
 {% if currentVersion == "free-pro-team@latest" %}
 {% note %}
 
-**Note:** Repositories using the legacy `<user>.github.com` naming scheme will still be published, but visitors will be redirected from `http(s)://<username>.github.com` to `http(s)://<username>.github.io`. If both a `<user>.github.com` and `<user>.github.io` repository exist, only the `<user>.github.io` repository will be published.
+**Note:** Repositories using the legacy `<username>.github.com` naming scheme will still be published, but visitors will be redirected from `http(s)://<username>.github.com` to `http(s)://<username>.github.io`. If both a `<username>.github.com` and `<username>.github.io` repository exist, only the `<username>.github.io` repository will be published.
 
 {% endnote %}
 {% endif %}