Minor documentation updates (#628)

* Make 3C documentation easier to find from the root readme.

* 3C build instructions: Clarify the working directory.

Author: mattmccutchen-cci

README.md

@@ -62,10 +62,14 @@ For more information on Checked C and pointers to example code, see our
 ## 3C: Semi-automated conversion of C code to Checked C
 
 This repository includes a tool called 3C that partially automates the
-conversion of C code to Checked C. Here is [general information about the 3C
-software](clang/docs/checkedc/3C/README.md), including development status and
-how to contribute. Here are the [usage instructions for the `3c` command-line
-tool](clang/tools/3c/README.md).
+conversion of C code to Checked C. Quick documentation links:
+
+* [General information](clang/docs/checkedc/3C/README.md), including development
+  status and how to contribute
+
+* [Build instructions](clang/docs/checkedc/3C/INSTALL.md)
+
+* [Usage instructions for the `3c` command-line tool](clang/tools/3c/README.md)
 
 ## More information
 

clang/docs/checkedc/3C/INSTALL.md

@@ -25,7 +25,8 @@ https://github.com/correctcomputation/checkedc-clang or
 https://github.com/microsoft/checkedc-clang (or, of course, a
 third-party fork, though we can't be responsible for that). Assuming
 you have already cloned one of these repositories, run the following
-(from the root of the working tree) for a basic build:
+(from the `checkedc-clang` directory or whatever you named your clone)
+for a basic build:
 
 ```
 # Get a copy of the Checked C system headers. Use Microsoft's