Add nlohmann/json to list of indi-qhy dependencies (#987)

* Add nlohmann/json requirement to README list

* Tweak requirements list for consistency and clarity

* Bump INDI minimum verison up to 2.1.0

indi-qhy/README

@@ -6,7 +6,7 @@ This package provides QHY CCD/CMOS and Filter Wheels INDI driver.
 Requirements
 ============
 
-+ INDI >= v1.9.6 (http://www.indilib.org)
++ INDI >= v2.1.0 (http://www.indilib.org)
 
 	You need to install both indi and indi-devel to build this package.
 
@@ -19,11 +19,18 @@ Requirements
 	libusb-1 is required.
 
 + libqhy
-	libqhy SDK is required.
+
+	libqhy SDK (located in ../libqhy/) is required.
 
 + fxload
-  fxload that can upload FX3 EZUSB firmware files is required. Some distributions include an old version that do not support the fx3 flag.
-  Compile a compatible version (https://github.com/lhondareyte/fxload.git) to support FX3.
+
+	fxload that can upload FX3 EZUSB firmware files is required. Some distributions include an old version that do not support the fx3 flag.
+	Compile a compatible version (https://github.com/lhondareyte/fxload.git) to support FX3.
+
++ nlohmann-json
+
+	@nlohmann's JSON for Modern C++ library (https://github.com/nlohmann/json) is required to build this driver using CMake.
+	It can be installed via APT as 'nlohmann-json3-dev' on Debian-based distros.
 
 Installation
 ============