Update Singularity build command in installation.md (#2273)

* Update Singularity build command in installation.md

`docker://multiqc/multiqc:1.20` is not the right URI, need to use `v1.20` as the tag instead

* [automated] Update CHANGELOG.md

* Fix other instance of same typo

---------

Co-authored-by: MultiQC Bot <multiqc-bot@seqera.io>
Co-authored-by: Phil Ewels <phil.ewels@seqera.io>

CHANGELOG.md

@@ -12,6 +12,7 @@
 - Picard: fix using multiple times in report: do not pass `module.anchor` to `self.find_log_files` ([#2255](https://github.com/MultiQC/MultiQC/pull/2255))
 - Remove unused dependency on `future` library ([#2258](https://github.com/MultiQC/MultiQC/pull/2258))
 - Fix incorrect scale IDs caught by linting ([#2272](https://github.com/MultiQC/MultiQC/pull/2272))
+- Docs: fix missing `v` prefix in docker image tags ([#2273](https://github.com/MultiQC/MultiQC/pull/2273))
 - Unicode file reading errors: attempt to skip non-unicode characters ([#2275](https://github.com/MultiQC/MultiQC/pull/2275))
 - Heatmap: check if value is numeric when calculating min and max ([#2276](https://github.com/MultiQC/MultiQC/pull/2276))
 

docs/core/getting_started/installation.md

@@ -241,7 +241,7 @@ docker run -t -v `pwd`:`pwd` -w `pwd` multiqc/multiqc multiqc . --title "My amaz
 
 By default, docker will use the `:latest` tag. For MultiQC, this is set to be the most recent release.
 To use the most recent development code, use `multiqc/multiqc:dev`.
-You can also specify specific versions, eg: `multiqc/multiqc:1.20`.
+You can also specify specific versions, eg: `multiqc/multiqc:v1.20`.
 
 Note that all files on the command line (eg. config files) must also be mounted in the docker container to be accessible.
 For more help, look into [the Docker documentation](https://docs.docker.com/engine/reference/commandline/run/).
@@ -297,7 +297,7 @@ This image was also renamed, versions up to v1.19 can be found at [`ghcr.io/ewel
 To build a singularity container image from the docker image, use the following command: _(change `1.20` to the current MultiQC version)_
 
 ```bash
-singularity build multiqc-1.20.sif docker://multiqc/multiqc:1.20
+singularity build multiqc-1.20.sif docker://multiqc/multiqc:v1.20
 ```
 
 Then, use `singularity run` to run the image with the normal MultiQC arguments: