Fix issue #4

_episodes/00-hpc-intro.md

@@ -52,7 +52,7 @@ Using a cluster often has the following advantages for researchers:
 * **Volume.** Many HPC systems have both the processing memory (RAM) and disk storage to handle very
   large amounts of data. Terabytes of RAM and petabytes of storage are available for research
   projects.
-* **Efficiency.** Many HPC systems operate a pool of resources that are drawn on by a many users. In
+* **Efficiency.** Many HPC systems operate a pool of resources that are drawn on by many users. In
   most cases when the pool is large and diverse enough the resources on the system are used almost
   constantly.
 * **Cost.** Bulk purchasing and government funding mean that the cost to the research community for
@@ -88,7 +88,7 @@ earliest days of computers, the only way to interact with early computers was to
 the 1950s to the 1980s most people used line printers. These devices only allowed input and output
 of the letters, numbers, and punctuation found on a standard keyboard, so programming languages and
 software interfaces had to be designed around that constraint and text-based interfaces were the way
-to do this. Typing-based interfaces are often called a **command-line interface**, or CLI, to
+to do this. A typing-based interface is often called a **command-line interface**, or CLI, to
 distinguish it from a **graphical user interface**, or GUI, which most people now use. The heart of
 a CLI is a **read-evaluate-print loop**, or REPL: when the user types a command and then presses the
 Enter (or Return) key, the computer reads it, executes it, and prints its output. The user then