minor readme enhancements

.gitignore

+# Editor's files
 *.swp
 *.swo
 *.pyc
+
+# Build artefacts
+/build/

INSTALL.md

@@ -112,12 +112,15 @@ To build the toolchain from source, one needs:
 
 ### Install build dependencies
 ```
+# Trusty and older
 VER=trusty
 echo "deb http://llvm.org/apt/$VER/ llvm-toolchain-$VER-3.7 main
 deb-src http://llvm.org/apt/$VER/ llvm-toolchain-$VER-3.7 main" | \
   sudo tee /etc/apt/sources.list.d/llvm.list
 wget -O - http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-key add -
 sudo apt-get update
+
+# All versions
 sudo apt-get -y install bison build-essential cmake flex git libedit-dev \
   libllvm3.7 llvm-3.7-dev libclang-3.7-dev python zlib1g-dev
 ```

README.md

@@ -47,6 +47,10 @@ many possible capabilities.
 
 See [INSTALL.md](INSTALL.md) for installation steps on your platform.
 
+## FAQ
+
+See [FAQ.txt](FAQ.txt) for the most common troubleshoot questions.
+
 ## Contents
 
 Some of these are single files that contain both C and Python, others have a