Update README.md

Clarify dependencies

README.md

@@ -23,11 +23,6 @@ Python3 script to manipulate FASTA and FASTQ (and other format) files, plus API
 ## Installation
 There are a number of ways to install Fastaq and details are provided below. If you encounter an issue when installing Fastaq please contact your local system administrator. If you encounter a bug please log it [here](https://github.com/sanger-pathogens/Fastaq/issues) or email us at path-help@sanger.ac.uk.
 
-### Dependencies
-  * samtools
-  * gzip
-  * gunzip
-
 ### Using pip3
 
 `pip3 install pyfastaq`
@@ -48,6 +43,12 @@ The test can be run from the top level directory:
 
 `python3 setup.py test`
 
+### Runtime dependencies
+
+These must be available in your path at run time:
+  * samtools
+  * gzip
+  * gunzip
 
 ## Usage