add missing development package to INSTALL.linux

fix whitespace

INSTALL.linux

@@ -18,6 +18,7 @@ $ make install
          - optional:  git
      (b) missing development packages
          - libusb-dev or libusb-devel or libusb-compat-devel
+         - libjpeg-dev or libjpeg8-dev
 
 2.2. Get the latest SANE backend from git:
       You can download "daily git snapshot" from here:
@@ -142,8 +143,8 @@ $ make install
       $ cd ~
       $ scanimage > test.pnm
 
-      
+
 3. Advanced Installation Information
 ====================================
 
-      Please read the documents INSTALL, README and README.linux.
+      Please read the documents INSTALL, README and README.linux.