Update install instructions

README.md

@@ -16,11 +16,18 @@ Primertrim requires vsearch, our recommended method of installation is through c
 ```bash
 git clone https://github.com/PennChopMicrobiomeProgram/primertrim.git
 cd primertrim
-conda env create -f primertrim_env.yml -n primertrim
+conda env create -f primertrim_env.yml -n primertrim 
 conda activate primertrim
+conda install -c conda-forge -c bioconda vsearch
 pip install .
 ```
 
+We also have a docker image available on DockerHub:
+
+```
+docker run --rm -it ctbushman/primertrim:latest ptrim -h
+```
+
 ## Algorithm
 
 Primer detection proceeds in three stages: complete matching, partial