popd: fixed description. Added in linux and osx. Removed from common.

pages/osx/popd.md

@@ -0,0 +1,15 @@
+# popd
+
+> Remove a directory placed on the directory stack via the pushd shell built-in.
+
+- Remove the top directory from the stack and cd to it:
+
+`popd`
+
+- Remove the Nth directory (starting from zero to the left from the list printed with `dirs`):
+
+`popd +N`
+
+- Remove the Nth directory (starting from zero to the right from the list printed with `dirs`):
+
+`popd -N`