Clarify documentation regarding 1.6.2

Due to not playing nicely with other versions, Arduino IDE 1.6.2 is only installed by install_ide when the user explicitly specifies it.

[skip ci]

Author: per1234

README.md

@@ -221,7 +221,7 @@ Some older versions of the Arduino IDE have bugs or limitations that may cause p
 - 1.5.5 and older - Do not support setting preferences (`--pref`), thus the sketchbook folder argument of `set_parameters` will not be used.
 - 1.5.5-r2 and older - Don't recognize libraries that have a library.properties` file that doesn't define a `core-dependencies` property. The file include is successful but compilation of sketches that use the library functions will fail.
 - 1.5.6 and older - `-` or `.` are not allowed in sketch or library folder names. If any are present the Arduino IDE will hang indefinitely when it's executed.
-- 1.6.2 - Moves its hardware packages to the .arduino15 folder, causing all other IDE versions to use those cores, some of which are not compatible. For this reason 1.6.2 has been removed from the default list of versions but may still be specified via the `IDE_VERSIONS` argument.
+- 1.6.2 - Moves its hardware packages to the .arduino15 folder, causing all other IDE versions to use those cores, some of which are not compatible. For this reason 1.6.2 is not installed when a version range containing, but not starting or ending in, 1.6.2 is passed to `install_ide'. 1.6.2 is installed if it is explicitly specified in a version list.
 - 1.6.3 and older - Do not support installing boards (`--install-boards`), thus `install_package` can't be used.
 
 #### Contributing