Create pwd chapter

build.rb

@@ -1,4 +1,5 @@
 chapter_name_order = ["introduction",
+                      "pwd",
                       "command-line-basics-part-two",
                       "finding-and-grepping",
                       "redirection-and-pipes",

en-US/src/pwd.md

@@ -0,0 +1,12 @@
+# pwd
+
+```
+pwd
+```
+
+This will tell you which directory you're currently in. In fact, `pwd` is short for "print working directory", which is asking the computer to tell you where you are currently. After pressing enter, your computer will answer your question.
+
+```
+$ pwd
+/Users/jessicard/just-enough-unix-command-line
+```