Fix upstream

Author: kwankyu

src/doc/en/developer/git_advanced.rst

@@ -45,7 +45,7 @@ out without requiring internet access::
     HEAD is now at f9a0d54099 Fix a slow doctest in matrix_integer_dense_hnf.py
 
 If it is not stored in your local git repository, you need to download
-it from the upstream repo first::
+it from the ``upstream`` repo first::
 
     [alice@localhost sage]$ git fetch upstream f9a0d54099d758ccec731a38929902b2b9d0b988
     From https://github.com/sagemath/sage

src/doc/en/developer/github.rst

@@ -143,7 +143,7 @@ If you already have a local Git repo and only want to link your fork as ``origin
     From https://github.com/alice/sage
      * [new branch]      develop     -> origin/develop
 
-You also add the Sage repo ``sagemath/sage`` as your remote "upstream"::
+You also add the Sage repo ``sagemath/sage`` as your remote ``upstream``::
 
     [alice@localhost sage]$ git remote add upstream https://github.com/sagemath/sage.git
     [alice@localhost sage]$ git remote -v

src/doc/en/developer/packaging.rst

@@ -957,7 +957,7 @@ We recommend the following workflow for maintaining a set of patches.
   commands.
 
 - When a new upstream version becomes available, merge (or import) it
-  into ``upstream``, then create a new branch and rebase in on top of
+  into ``upstream``, then create a new branch and rebase it on top of
   the updated upstream:
 
   .. CODE-BLOCK:: bash
@@ -1052,7 +1052,7 @@ Sage mirrors when a new release is prepared.  On GitHub PRs
 upgrading a package, the PR description should no longer contain
 the upstream URL to avoid duplication of information.
 
-Note that, like the ``tarball`` field, the ``upstream_url`` is a
+Note that, like the ``tarball`` field, the ``tpstream_url`` is a
 template; the substring ``VERSION`` is substituted with the actual
 version.